Because they don't respect you, your time, or your agency. They think they own you, and to some extent they do. At least enough to force you to live in near certain place, and then be at that place every single day for as long as they tell you to. Regardless of the cost to you to make sure you are there when they want you to be
Try and tell your doctor, waitress, or mechanic that their workplace doesn't respect them for making them come into the office, and wait for your common sense to kick in.
How is that any different than a company expecting you to work for them for 40 hours a work? The whole point is that they're paying you $$$ in exchange for your work. If your work includes being at the office, that's part of the exchange. If an employee doesn't want that, they don't have to take the job (which is what's happening).
Turns out the "you being in the office" is often redundant. The employees now have a proof ("my work output hasn't decreased during covid") and want to renegotiate their contracts.
Companies that disregard what their employees want or need are not the companies I'd want to work for.
Of course, sometimes, there's no other way. "We work for the US government, they require us to come to their offices to get access to X". That's fine. A lot of the times, it's entirely different.
For example, Morgan Stanley blatantly disregards what employees want:
"“But [on] Labor Day, I’ll be very disappointed if people haven’t found their way into the office,” Gorman said. “Then we’ll have a different kind of conversation.”" [1]
This, I feel, often projects into different kinds of issues. You taking an unexpected PTO might be a problem. In my mind, it is emblematic of a work culture that de-humanizes their employees. And that is great to know--so that I can avoid those companies.
> The employees now have a proof ("my work output hasn't decreased during covid") and want to renegotiate their contracts.
Are you sure? Plenty of companies have experienced lots of issues with communication and velocity during covid. I don't think you can declare, in general, that WFH was not a blow to productivity. Granted, I don't think you can declare that it _was_, but it certainly seems dependent on the type of person and the type of company. Your experience is not everyone's.