[slg]

From a census of homeless people in LA county a few years back[1]:

15% of LA's homeless population has substance abuse problems. Only 12% of these people are in shelters.

25% have serious mental illnesses. 20% of these people are in shelters.

Overall 33% of homeless people are in shelters.

So you are partially right that drug use and mental health issues can make sheltering some people more difficult. But you are very wrong that people with either of these issues make up a majority of all homeless people. It is just classic confirmation bias in that people with these issues are the most visibly homeless. The people who are living in their car or a shelter and simply can't afford a home aren't easily identifiable as homeless when you walk past them on the street. This can also be seen in the previously linked data as only 28% of LA's homeless population qualifies as chronically homeless.

Basically you are only able to see a small portion of the problem and are assuming that is the whole problem when in actuality homelessness is roughly 4x worse.

[1] - https://www.lahsa.org/documents?id=3423-2019-greater-los-ang...