Speculation is not really the issue, most of the issues are around regulations limiting construction.

If you wanted to incentivize home buying for young families, then the demographic that needs the most incentives are old people whose kids moved out decades ago. Every single person I know has two aging parents living in 4 or 5 bedroom homes by themselves, my own included. I know people are sentimental about the homes they grew up in, but this is the biggest lever you could move: hike property taxes on properties with unused occupancy.

If you want to keep the home in the family, then this encourages the parents to give the home to one of their kids who actually need it because they're starting a family of their own.