For us it varies dramatically by team, but the problem is a WFH policy needs to be company wide for the most part. All it takes is for a few teams to cause a problem for everyone.
>>people in the office often aren't particularly productive either.
Some of that depends on how you define "productive", having non-work related conversations while in the work place may not be "productive" but it is team building
Watching netflix, or doing your laundry when you should be working on a report is neither team building or "productive"
Further lots of informal conversations are how many many many many business decisions are made, and how lots of information flows through a company.
So many times I have been made aware of new projects, changes, or other things happening in the company simply because I happened to see someone in the hall and they happen to mention it... That would never happen on a formal call. meeting, etc in a fully remote environment.