Investors buy on the order of 25% of all residential real estate available. Big money uses its leverage to do this in order to raise the prices (due to the scarcity that they are helping create), which they then use to drive up rents or flip properties at a profit. This cycle has been on repeat for several years now. This is why you see people doubling and tripling up living together and it won't stop until they can't do it anymore or our legislators decide to do something about it which I don't even know why I bother saying it like there's any chance they will.

Foreign ownership of US property is certainly a significant percentage of that equation, but there are other reasons why its important to pay better attention to foreign ownership. Allowing foreign interests unrestricted access to property in the States ends up giving us stupidity like Saudi Arabia feeding its cattle alfalfa grown in Arizona. One of the most water-intensive crops in existence that its own government won't allow it to grow itself, is grown instead in our desert, while our own citizens get their water cut off.

Edit: it may technically be "supply and demand" when 25% of everything available is bought with the intention of making a profit on it rather than providing a place to live - but it isn't beneficial to the citizens of this country when the whole world and all its big business interests can compete with individuals to buy housing.

Yes, lack of housing is the bigger issue. Here in the Boston area, it's pure supply and demand. Neighborhoods are full of triple-deckers just off the city center that could be denser apartment buildings. Landlords can charge whatever they want, because they know that anyone who wants to live in the area will have a hard time finding another place.

There's also the question of transit infrastructure. Even with less dense housing, if there were easy ways to get around other than cars, proximity would be less of an issue.