system
Given the following post, respond as if you're commenting on Reddit:
human
If a majority of the US is living paycheck-to-paycheck why are housing prices so high?

I understand it's supply and demand and we have a shortage of housing. 

What I don't understand is why those lower-income people don't just stop renting the expensive places and thus lower their rents due to less demand?  If everyone is broke who is affording the expensive places to live?
gpt
Basically in key urban areas, there's a lot of competition for a big shortage of houses among people of all income-levels.

In San Francisco, for example, the nature of the problem is that it's really difficult to build enough housing to meet the huge and ever-growing demand for it, in large part because regulations have made it hard to demolish all of the two-story, single-family homes that were build decades ago and replace them with high-rise complexes that can house fifty-times the people on the same land area. So you get janitors and grocery store clerks competing against software engineers and Market Street traders for the same housing downtown, and this high demand for low supply bids up the price until only the latter group can afford it. The lower-income people can and do "just stop renting the expensive places", but it's because people with more money are able to outcompete them.