A more savvy (or less short term) take is that these places are able to negotiate favorable leases right now. Once office space fills up again, those prices will go up again.
I think the real reason lies between "butts in seats" and layoffs.
I also feel like there is a class of management that feels good about themselves by having subordinates observe them with all the trappings of their office. These are the people that want a dress code and spend money to look good at work even if nobody ever sees a customer. They have to have the bigger office -- not out of need -- to demonstrate their position. Bigger desk. They might have a better computer than developers even though they never use anything more taxing that Excel (this happened a lot more 20 years ago, less today). These people want to return to office, otherwise nobody knows how much they are in charge of.
I think the real reason lies between "butts in seats" and layoffs.
I also feel like there is a class of management that feels good about themselves by having subordinates observe them with all the trappings of their office. These are the people that want a dress code and spend money to look good at work even if nobody ever sees a customer. They have to have the bigger office -- not out of need -- to demonstrate their position. Bigger desk. They might have a better computer than developers even though they never use anything more taxing that Excel (this happened a lot more 20 years ago, less today). These people want to return to office, otherwise nobody knows how much they are in charge of.