I don't agree with my grandmother, but she had the following to say about this:

Single-family homes in subdivisions are A) essentially pretty breeding cages for companies, who are a significant percentage of campaign donations I would assume, and B) exist at the cultural intersection of that concept called the "American Dream" which is still politically an OK thing to support and enable, likely due to the fact that most voters are boomers or older who actually had a decent chance at living that dream.

Personally my point of view is the following: the nuclear family is the indivisible unit of society, and should be the only social policy supported by politicians - housing that directly supports this goal is the only valid housing that should be allowed. The more efficiently we can build it, the more families we will have and the better the economy will be. Otherwise society would become selfish; we would eventually degrade into tribal-style warfare; and then finally become a low-trust society, which would make us a weaker country.