Employers are stuck with huge rents and rates in their rented posh offices and can't get out of the contract for years. Why pay for dead space, get bums on seats to justify the costs.
Managers need staff around them to feel in control. Let's not forget the micro-managers.
I'm lucky I'm in IT. I've worked on PCs all round the world from home in the UK since 2005, going into the office a few days when I wanted. Even after changing jobs, I still only go into the office once a week.
Am I and my colleagues productive? - extremely, in fact I work harder at home where I can focus than I do when I am in the office where I can be distracted by people who want to chat and catch up.
BUT. Going into the office can be beneficial. In the office I was able to raise a complex problem before several of the team I am in on the fly a day ago and 10 mins later it was sorted. Face to face can be greatly beneficial.
Just one point though. If companies are claiming Zero Carbon Emissions - Bollocks, if you are forcing people who drive cars, ride buses burning diesel to come to work then by default that company should incur the emloyees emissions their transport give off. IMOO