I think part of it is the drug war and how drug users are viewed. People associate homelessness with drug use, and therefore seem to think it's deserved. (Furthermore, if you are a drug user who doesn't want to go with abstinence, your options assistance wise are limited)

Also tbc the assumption people make about homeless people being drug users is incorrect. I just think it's a big piece of how it's been normalized

In my experience, as someone who has been homeless, the homelessness or housing instability often comes before the chaotic drug use.