Some people I know who supported the march do so because they're upset at the upcoming spare/unused bedroom tax, which aims to bring more homes on the market to lower prices. They don't care about housing people, they care about profit.
I'm also not convinced cutting immigration would help at all when it would only discourage construction, which is already below what's needed to support birthrate + people moving in from rural areas. Immigration isn't the cause of the crisis, so cutting it isn't the solution.