Because then the gov't can step in, buy up housing and "provide" it to the people at an "affordable" rate.
Communism sells based on the idea that you personally will no longer have risk or be denied the things you like. "If you just allow communism, you'll have your nice house no matter what happens in the market - EVERYONE will have a nice house".
If the markets collapse and the gov't can step in (as we saw in other countries such as England just after ww2) then the gov't gains more control over people and people get used to the gov't handling all their affairs. Pretty soon people become afraid to do anything on their own and become entirely dependent on the gov't.
Remember - there is no more effective way to enslave people than to provide for their every need.