They've invested a lot of money in office real estate and hate that it's going to waste.
Also, CEOs tend to be extroverts who want to be around people. They're also sociopaths who think everyone is like them (or they don't care what others think).
If you work from home and only work for 4 hours, lots of managers do not know how to tell if that work you did took 8 hours or 4. In the office they have plausible deniability that they saw you there doing something.
They've invested a lot of money in office real estate and hate that it's going to waste.
But see this makes no sense. The money invested is gone (or contractually tied up). Using it won't make it a good investment.
It's like if you bought a car and then moved somewhere where you're like 1 minute walking from work, the grocery store, the hair salon,.and the best restaurants, and you never travel otherwise. The money spent on the car is objectively wasted. Using your car unnecessarily to drive places you (a) wouldn't normally go to or (b) don't need a car to get to is not only pointless, but actually costs MORE MONEY because of gas and maintenance (or for a building, energy and cleaning).
Ahh. Didn't know about the tax breaks. Makes sense. You know, as much as if "makes sense" to be forcing people to spend more time and money traveling instead of working or spending time with their families.
No idea whether it's their reason, but anecdotally I've found it has a few benefits. If coordinated properly it's significantly easier to train new(er) staff, it improves cross-organisational understanding to overhear other departments' conversations either at desks or in break rooms, and it stops people becoming isolated pockets of knowledge and culture because they only ever see or interact with the same one or two people.
Because the people creating these mandates don't have to suffer them. They come and go as they please, and they don't work in the pit open office space. They have real offices with furniture, walls, and doors that shut.
I can help you. The benefit is strictly for the maintenance of th bullshit status quo and the logic is, once you're already coming in two days a week, it'll be an easier fight to ask for a third. Then a fourth. And so on.