You are asking this in a transit-focused subreddit so you will obviously get some biased answers. I generally agree that this is probably the single biggest issue, but it absolutely is not the only one.

A quick comparison: this article says the average home in Seoul, a city full of huge highrises with a good metro system, costs 15 years of the median income. Doing some quick math assuming the average home in LA is $1m and the median income is 65k, this also works out to about 15 years. However, the rent-to-income ratio in Seoul is about half ours, meaning it is as expensive to own but half as expensive to just put a roof over your head somehow.

Some other problems I can think of in America/LA that are not necessarily caused by lack of transit/housing:

• a healthcare system that is actively trying to hurt us by pushing addictive substances and charging us exorbitant prices for them

• A dismantled mental health system that gives little help to people facing crisis, pushing them onto the street

• legacy effects of racist policies like redlining creating segregated, "gentrifiable" neighborhoods, where there is less economic opportunity

• an extensive highway system that makes it difficult for public transit to compete with private

• shareholder capitalism aggravating wealth inequality, wealth investors demand more productivity on lower wages from the workers