Plenty are, it’s just that the largest companies built those places, they cannot trivially liquidate them. Plus they usually own the whole land, so cutting part of it away is not easy.
They still should. For many jobs office work is a completely unnecessary waste of:
Productivity (via constant distractions)
Time (commuting)
Money (via the building maintenance costs)
Space (the actual building)
Resources (heating and shit)
But managers are loathe to ever admit any failings, our market culture frowns upon this. Hence admitting that your building is no longer needed is not a thing any manager to wants to bring up in a meeting to their bosses, so back to the office it is. :<