In its heyday a few years ago, WeWork said it would reinvent offices. But the company never created a sustainable business or changed how most people worked.

The business of offering flexible office space on short leases to individuals and businesses, a model that WeWork hoped to make mainstream, remains a niche in commercial real estate despite the billions of dollars the company and others invested in the approach. Flexible office space accounts for less than 2 percent of all office space in the 20 largest U.S. markets, according to Cushman & Wakefield, close to its share before the pandemic.

WeWork filed for bankruptcy protection this week in an effort to quickly slim down its portfolio of office spaces. The company wants to give up over 70 leases right away, with possibly more to follow. Other co-working companies may take over some of those locations, but some owners of office buildings said they were not expecting this approach to ever amount to more than a small part of their business.

Many employers are paring back their office space because workers aren’t going in five days a week after growing accustomed to working remotely or on a hybrid schedule. Office vacancies are at their highest level in decades, with lots of space available for sublet often at a deep discount from the rents that prevailed before the pandemic. WeWork’s bankruptcy will only make the situation worse by leaving landlords with more space to fill.

Michael Emory, the founder of Allied, a real estate investment trust that owns office buildings in Canada’s largest cities, said flexible office providers would always exist, providing space for smaller companies to operate without signing long leases. But he said it would never make up a third of all office space, as JLL, a real estate services firm, predicted before the pandemic would be the case in 2030.

“There wasn’t a snowball’s chance in hell of that happening,” Mr. Emory said.

He said office landlords would keep offering space to co-working firms in some buildings because they attracted tenants that might grow and want to lease their own space in the future.

David O’Reilly, the chief executive of Howard Hughes Corporation, a developer focused on large developments that often include homes and offices, said co-working was a nice amenity for some tenants but wouldn’t take over the commercial real estate business by a long shot.

“When co-working becomes a disproportionate amount of the building, they become directly competitive with the landlord,” he said. Howard Hughes has two leases with WeWork, and Mr. O’Reilly said he was talking to other co-working providers about taking over the space.

Still, some co-working executives said they expected to do much better than WeWork because they were pursuing a different business model. WeWork leased millions of square feet from landlords, hoping to take in enough revenue from its customers to cover its costs. But that never happened, leading to multibillion-dollar losses.

Other co-working firms say they don’t lease their space, instead operating offices for a set fee or a cut of the profits. Co-working companies using this model are less likely to collapse, but it can also mean they earn less when times are good.

“By sharing the profits with the landlords, it allows us to do a lot more,” said Mark Dixon, the chief executive of IWG, which was one of the first companies to offer flexible office space in many locations and which operates several brands, including Regus.