SF homeowners want their neighborhood to stay locked in time forever and pretend nothing will ever change. They want to protect the "character" of the neighborhood, by preventing all high rises and anything that isn't a single family townhouse.

They'd probably be fine with more housing being built 'somewhere else' for the homeless. But ya know, definitely not in THEIR backyard.

Developers (aka landlords) aren't the ones protesting new building being built. This is because they would love to be able to build more. Even though they would make less money per apartment, there is so much demand for houses, that the massive amount of new development would make up for it.

There is only so many landlords out there. Their vote isn't particularly significant. But there are a LOT of NIMBY homeowners.