This is really the crux of it, pairing enforcement with housing, emergency shelter, and treatment is the way to go.
There's a genuine question to ask...if you've offered someone all the support you can muster to move into their own apartment, fully paid for with support staff on site, and that person says no, they'd rather live in a tent in the park, what options are left?
I totally understand turning down emergency shelters. They can be crowded, difficult places. But when you're offering people their own rooms and they say no, what do you do next?
Finland is a very different place than California. If you don't have your wits about you outdoors in Finland for at least 3 months of the year, you will die. The weather, in a way, forces solutions on people. Finland is more comparable to Minnesota in terms of weather, population, and size, and the issue of homelessness in Minnesota pales in comparison to California.
Finland also has universal healthcare, and it's hard to overstate how impactful easy access to competent mental health and substance use treatment is.
In California, you can wear shorts all year, and mental health and substance use treatment are difficult to access and largely administered by for-profit companies providing awful care.