It's not an even playing field when you have to organise a mortgage, wait for an inspector, most likely arrange a buyer for your current house... all of this takes a lot of time.
Private Equity can avoid all the waits and just buy it as a cash sale, sight unseen.
Of course, it wouldn't actually be that much of a problem if there was sufficient supply of new housing. Lots of talk about building more housing, but not enough 'fuck the NIMBYs, we're just DOING it'.