If there's an unsavory reason, I think it's one or both of:

1. Employees slack more on average working from home. Employers want people stuck in a work-only place where they're monitored. Same as how open offices replaced cubicles "for cost reasons." I've seen evidence of this at my job.

2. They're heavily invested in physical offices in particular cities already, so much that they alone can sway the same real estate market they're invested in, and it's not a sunken cost yet.