A significant number of the homeless in LA (by some estimates as many as half) choose homelessness over shelter because almost all shelters in LA have sobriety requirements (meaning no drugs or alcohol).
There are hundreds of shelter beds in LA that stay empty each night because the homeless who would occupy those beds would rather pass out on the street to their drug of choice.
I also don't think that is the only issue with shelter usage. In Denver, a common complaint I hear is that they choose the street over the shelter because they feel both their physical safety and their personal belongings are more secure on the street. I also try to think about this from my own perspective and if I was in that situation, I'd rather find a "place of my own" on the street over a shelter shared by tons of people (unless it was really cold out).
LA has the same problem with its attempts to "solve" its homelessness problems, which are at their root zoning problems: http://seliger.com/2017/08/30/l-digs-hole-slowly-economics-f...