SAN FRANCISCO — The tech sector is, increasingly, embracing the language of urban planning — town hall, public square, civic hackathons, community engagement. So why are tech companies such bad urbanists?

Tech companies are scrambling to move into cities — Google will have a larger presence here. VISA and Akamai have ditched the suburbs to come here. Tech tenants now fill 22 percent of all occupied office space in San Francisco — and represented a whopping 61 percent of all office leasing in the city last year. But they might as well have stayed in their suburban corporate settings for all the interacting they do with the outside world. The oft-referred-to “serendipitous encounters” that supposedly drive the engine of innovation tend to happen only with others who work for the same company. Which is weird.

There’s been no shortage of published laments on the changing nature of San Francisco over the past several weeks, so I’m loath to add another complaint to the list. And yet … I keep coming across instances where the tech sector flocks to the city and talks of community yet isolates itself from the urban experience it presumably couldn’t wait to be a part of. The other week, for example, I had an appointment at Hills Plaza, a waterfront complex that quietly houses an ever expanding Google outpost. A year or so ago there was a Starbucks at street level, and while that in itself is of course not unusual, there weren’t any other cafes in the neighborhood, so I’d often walk the two blocks from my office to get coffee there. It was a nice excuse to take a walk and interact with the world outside my work space.

Today, that Starbucks is gone. So is the popular brewery that was next door to it. The sandwich shop across the plaza is closed, as is the salad bar. It’s not that any of these businesses were particularly distinctive or delicious, but they provided a valuable service — lunch — and also some social connection among the building’s tenants and people in the immediate neighborhood.

Gone also is any sign of life the plaza ever had. Google leased as much of the complex as it could get its hands on — and the correspondingly skyrocketing rents accelerated the closing of all the ground-floor businesses, even a short-lived outpost of The Melt (a franchise that serves uniformly grilled sandwiches made with a high-tech — and tech-industry-financed — piece of machinery). In place of Starbucks there is now something called the Mozilla Community Space — that isn’t open to the community. You need to be a registered “Mozillian” (whatever that is) to gain access.

Tech companies that remain in the suburbs are taking a similarly upside-down approach to urbanism. Facebook’s Menlo Park campus, set in a sea of parking, is a sort of movie-set version of a city, with cafe, dry cleaner, doctor, dentist and personal trainers all accessible only to employees. Informal public gathering places (like Starbucks, for example, or a barbershop) are essential to local democracy and community vitality. But by creating “third places” (home and work are the first and second) that aren’t actually open to the public, that benefit is severely compromised.

“Community space” implies something that is open to, well, the community. Subverting of naming conventions to suggest public access and transparency, while providing neither, is troubling and increasingly pervasive. But this turning inward, despite the incessant drumbeat of “community,” is quickly becoming the rule rather than the exception.

Take Twitter, which recently moved into new headquarters in a long-vacant high-rise on Market Street in one of San Francisco’s poorest neighborhoods. The company’s decision to stay and expand in San Francisco was controversial (Twitter received considerable — and highly controversial — tax incentives from the city and overwhelming support from Mayor Ed Lee), and it was expected that the company’s presence in a depressed section of a major thoroughfare would help revitalize it.

A walk though that neighborhood reveals that this has yet to happen. Twitter employees are fed breakfast, lunch, dinner and snacks on site. (Their in-house dining area is, of course, called “The Commons.”) As such, they have little incentive to leave the building. This would seem to be a perk, but think about it: mealtime was once a break from work, now it’s just an extension of the workday. The building has no ground floor retail (apart from a pre-existing Walgreen’s) — though plans for a market and at least two upscale restaurants are underway. Potential new proprietors of, say, a new cafe, pizza place or boutique are kept away by the area’s now skyrocketing commercial rents — though many buildings remain vacant as landlords hold out for the highest bidder. Even if they could afford the rent, small businesses also understandably fear opening a business where pedestrian activity seems limited to the beginning and end of the workday.

What is emerging in the neighborhood is a strong uptick in evictions — there was an increase of 38.2 percent in 2013 from 2012. (Per their community benefits agreement with the city, Twitter has been donating a nominal number of legal assistance to some neighboring residents facing eviction.) This city may be the fulcrum of innovation, but little of its disruptive thinking is doing anything to address that urban reality.

Indeed, the physical manifestation of the “public square” — another favorite civic concept embraced by the tech sector, up there with “town hall” — alas is most visible in the large numbers protesting the city’s record-breaking number of evictions.

In “The Death and Life of Great American Cities,” Jane Jacobs wrote, “Cities have the capability of providing something for everybody, only because, and only when, they are created by everybody.” We’re losing that here. The further the tech sector gets from the reality of the problems it’s engaging with, the smaller piece of the problem they’ll end up actually fixing.

The tech sector’s embrace of urbanist lingua franca and its enthusiasm to engage with urban problems is awesome, and much welcomed. But these folks need to become better urbanists.

Some are: Zendesk, located in the same neighborhood as Twitter, has donated $5,000 to a nearby community garden, has been doing about 40 percent of its catering through local businesses, and has invited local groups to be guest lecturers, among other community outreach efforts. I’d especially like to highlight 5M, a mixed-use project at San Francisco’s 5th and Mission that is determined to be a public asset as much as a private sector one. 5M shows that tech (and non-tech) companies can become an essential part of the urban fabric in a way that satisfies employees and their neighbors. The project houses tech companies (most recently, the mobile payment company, Square, which is moving down the street; their space will be taken over by Yahoo engineers) but also The San Francisco Chronicle. This is a much more outward-facing endeavor: With weekly food trucks at lunchtime, numerous public events hosted by their tenants, which include TechShop, HubSoma (a co-working space/tech incubator), and Intersection for the Arts (a gallery), 5M builds on the vitality of public space and the people who activate it.

And an even simpler way to contribute to the vitality of the urban fabric? Invest in and introduce a small manufacturer or business that makes something the neighbors can use in the physical — not the digital — realm. That’s what Jack Dorsey (C.E.O. of Square, which he founded in 2009) did when he became an investor in Sightglass Coffee, a cafe and roastery. It not only gave him a way to beta-test his product but, as the cafe was located a short walk from his office, gave him a place to go for his daily dose of caffeine. It gave a lot of other people in the neighborhood a place to go, too. Maybe he can do that somewhere near his other company’s office? It’s Twitter.