That’s a decision of employers, not policy makers

Until they decide to make it their decision and do something like tax companies per onsite worker and/or increased property taxes for office space that could have been better used. Lots of options.

Cities also have their own perverse incentives to maintaining the 9-5 downtown status quo. A whole host of businesses depend on these workers and they are involved in the chamber of commerce and various other orgs city leaders listen to when making decisions.

So you drive the office workers out of the city and then what do you do with the other commercial business? They still commute or you raise taxes enough for the city center to die out and hope for suburbanization?

You tear down those old, unsafe office buildings (we have lots of them in our city) and put up modern mixed use buildings. More people == more workers == more customers == more businesses. Add in some cultural features and you have a vibrant downtown that doesn't rely on commuters and doesn't become a ghost-town after 5:00.

Or even better, spread out work for those who can't work from home.

I live in a small country, where a lot of jobs are in the capital, A LOT of people drive to the capital daily (20, 30, 50, even 100km one way), and complain about it... and complain how everything is there, complain about centralization, etc...

..and then also complain when a company in their smaller city wants to expand or when someone wants to build something new there. Also complain against the current companies that exist there.... even though their house was built due to closeseness to that factory in the first place (like whole neighhbourhoods that were built by workers in that company nearby, and now, 30, 40 years later, their kids want the company to close, due to a lot of random reasons).

for americans: not all tech has to be in california, other states exist too

A lot of american metros are polycentric with their job markets already. That was one of the sells of suburbia: spread out and therefore lower the congestion that was bogging down urban areas at the time. There was a time when it was predicted manhattan would flood with manure in the future should horse traffic increase how it had been. Then of course the car came but still, these were concerns even back then. Someplaces instituted height limits to attempt to spread congestion too, especially done in europe where many cities today have denser urban sprawl but its pretty clearly capped at a height limit which forces it out.