system
A chat on subreddit /r/me_irl
human
Most houses are still bought by owner occupants. It's people who got into the market when starter houses were still a thing trading their equity around with each other and young professionals making enough or with enough family support to still buy a first home at elevated prices. 

Corporations make it worse but are only a piece of the problem. Supply, and supply of new starter homes in particular, largely due to zoning restrictions, is still a much bigger issue.
gpt
There's a lot going on. People stay in houses longer. Corporations buy up houses en masse and then would rather have them sit empty than drop the price to sell. Construction doesn't print money and shit gold bricks like it did 20 years ago so a lot of people got out of it despite it being very profitable. Wages are down and rent is up so getting down payments is a nightmare.

It's just a perfect storm of greed. I don't know who to blame but I'm going to go with the guys who cried that they couldn't afford their 20 mortgages with the rent freeze, i think we could probably put those guys on a one way trip to Siberia in flip flops and a Hawaiian shirt.