I could set up my place to be both a home and an office, but it wouldn't be cheap (for starters, I'd want to rent something bigger). Considering taxes, this would be equivalent to at least a 20k pay cut due to costs being offloaded on me.
I totally see why employers love that.
Additionally, FAANG and startup tech offices often serve as more than an office - they tend to have a lot of shared amenities that are just not practical to have at home. I don't use a 3D printer often enough to own one, but there is one in the office. Gym? Office, and it has more than a pull-up bar. Post office? Office. Inbound packages? Post office. In the office. Grocery shopping? Happens much less often if you eat out. In the office. Why would I want to eat out of my own fridge and pantry (and have to prepare the food myself) when I can grab tasty food prepared by people who actually know what they're doing?
The benefit isn't just that the stuff is free; the benefit is that it's all right there. It's an incredible time saver.
If the office is just an office with no amenities, you have a sucky commute, or you have a family, then I can see why WfH would be attractive. However, if you're young and single, have a nice office, this is going to suck.