I can't remember exactly what I was reading, but after the trend of open office plans to increase cooperation and collaboration started, studies looked at the effects, it turned out everyone was getting massively distracted and wasting time and non-productive busy work increased because employees felt they were being constantly observed. If anyone's ever spent time around tech companies where employees are encouraged to wander around and "collaborate" all day, you see people just pissing about not doing anything. All the work gets done once they cloister in their office/at their desk and clamp down on their tasks.
WFH is the best thing that ever happened to my work productivity - I have so much more free time, I was able to go back to school. I can focus on my work when I am working instead of having errant conversations, getting side-tracked by random unimportant tasks, and constantly leaving my desk to go have 20-30 minute conversations that can be summed up in a 3 minute e-mail. Give me my tasks and leave me alone. I typically finish an entire day within two hours if I'm left alone. The rest of the day is usually punctuated with phone calls that need action/following up and group meetings that I do not need to be present for 50% of the time.
If my job asked me to come back full time, I'd probably quit. I have savings. I can chill until school is done and get a job in my new field.
Management just doesn't like having less control. My philosophy is, "Is the work getting done? Then don't worry about what I'm doing over here."