That doesn’t mean “is a symptom, not a cause.” If it’s actually supply and demand, then the investors buying the housing is part of the problem, not just a symptom. The investors are decreasing supply and increasing demand, so it’s really two sides of the same coin.
Personally, I think that just building more houses isn’t the answer, because the corporations can just keep buying them up. This will continue to artificially decrease supply and increase demand, which keeps them making a profit. And as long as corporations can make a profit with this model, they will (and people will continue to suffer).