Because there are plenty of older workers who want functions to remain as they always have and therefore they equate WFH as not working.
There are also management types that believe people need the "energy of the office" (an actual term our office used to to try drag people back in during the height of COVID) to thrive. From my experience those who need "the energy of the office" are hyper-extroverts who spend most of their time engaged in mindless chat.
That's pretty ageist? I'm in my fifties. Friends I know that WFH are my age and older up to 70 odd.
When we chat, we all agree we are far, far, far more productive working from home (We work in IT)
I can help up to 5 or 6 people at a time at home while still doing my own work. If I were in the office and I helped someone then it would be literally impossible for me to do my own work as I'd be engaged with them and absolutely impossible to help the other 4 or 5 people that wanted help. If you are in the office and you are with someone then they 100% monopolise your time.
The few times I've been in, my work rate has dropped to (being generous) maybe 5% of what I can get on with at home. Would be probably more accurate to say 2% actually. I just get hassled then sit with someone all day, get nothing done, everything has to be explained in detail and it's absolute shite.
When I'm at home, people drop me messages and I go and fix stuff for them, or drop a one or two-liner and they work it out for themselves. If you're next to them, they learn nothing, you just end up doing their own work for them.