Most shelters have serious problems, like mold. They aren't actually safe because you can be harassed, assaulted or have your stuff stolen by other homeless people.

A high percentage of homeless people have health issues. This means putting a bunch of them together exposes already sick people to cross contamination with other diseases, making their health worse.

They have curfews and other rules making it one step removed from a prison. If you have any funds of any kind, some will charge you for being there, making you essentially their prisoner with no means to escape.