I doubt developers are especially resistant to building apartments. It’s probably a zoning issue that makes it more expensive for them (because upzoning would often be needed, which currently increases land value due to the higher income potential for the owner). That’s why there was recent talk about making cities open up zoning. But if they don’t address that upzoning increases land value, then it could make rents for these new places prohibitive if just left to market forces. (Places with low rents and high quality homes don’t just have a high supply-- they generally have robust options for non-market housing.)