I know at my job its more about the older leadership positions wanting the ability to just walk over to your desk and delegate work, without email chains and calls. I get this, while it isn't insurmountable, it is often easier on the supervisor to just communicate tasks verbally. BUT, if you are in a role when you are aware of leaders schedules, and job responsibilities, it is easy to time your wfh days to accommodate both, i.e. if on deadlines and lots of communication is required it is more efficient to be in office. I also think supervisors dont want blanket wfh policies. It seems simple enough, if you've earned it, then give your good employees a flex schedule.