My first thought was that by making it more difficult to enter the city you don't actually encourage people to move to the city but rather to get a remote work job so they never have to go to the city again. Which in turn speeds up the decay of the city by killing restaurants and all the other businesses these people used to go to.

Like you said, we're already seeing large cities lose population as people get "work from home" jobs and move to less dense areas.

Overall I don't think people are not living in cities because there aren't enough green spaces. I'd assume that if you polled people on why they don't want to live in Baltimore the top reasons would be taxes and crime with green spaces not even breaking the top 5.