That is not clear to me at all. What I have learned from schooling is that this is a supply and demand problem and that if you want the price of housing to be less you need to either raise the supply or lower the demand.

This conspiracy theory that people who own real estate are limiting supply so their investments go up is not reality. People indirectly want to limit supply because they enjoy their neighborhood the way it is. It turns out what they enjoy about their neighborhood others enjoy about the neighborhood so the price goes up. It doesn't mean that they are overall goal is to increase the value of their house. The evidence is that adding public transport and rezoning to higher densities and commercial use would increase the value of their property a lot but most oppose that because that is not why they bought in the neighborhood.