It's fun to blame the super rich but I'd say it's fundamentally due to a combination of population shift from rural to urban areas

https://ourworldindata.org/grapher/urban-and-rural-populatio...

and normal homeowners stopping densification out of fear of reducing the value of their own home or just not wanting the riff-raff living near them. These people are really the ones doing a directly harmful thing for pure selfish greed. They're not super-rich, they're just people's parents. But they're trying to make money by excluding others instead of doing anything useful.