Rent increases are terrible for renters (and I rent), but great for homeowners (in that they generally track rising real-estate values.) It's mostly just a matter of perspective.
Nobody seems to complain that the housing market in SF is on fire for the same reasons that rents are up.
It's not just SF... a lot of people complain about the Bay Area housing market in general - just not the sellers.
Even if you can afford to buy a house, it's damn near impossible to find one because sellers are getting many offers on the first day/week (a lot of which are in cash). And a lot of these offers aren't from homeowners, but rather investment companies. There was a good article in the SJ Mercury News last month about it [1]. Even if you want a house (and can afford one), the market just doesn't have enough supply, so people are then stuck renting. It really is a pretty big problem.
It's probably because homeowners are (almost always) voters in a district, whereas potential home buyers probably aren't, and renters are somewhat less likely to be than homeowners. You'd expect policies designed to keep homeowners happy.
Nobody seems to complain that the housing market in SF is on fire for the same reasons that rents are up.