The same as with vancouver, San Francisco and Los Angeles are both some of the rare large cities in the USA where a homeless person can live a fully outdoor lifestyle year-round and not risk freezing to death.
This is often repeated, but the entirety of the US south is warm year-round and the proportion of unhoused homeless is much lower in all those southern cities. Clearly there is something else at play on the west coast that resists housing the homeless.
Turns out the homeless, like many (most?) people, prefer living in desirable places.
When you have no ability/intention to pay rent, the whole cost of living deterrent vanishes.
So it seems rather obvious to me you'd have a higher rate of homelessness in the most desirable (most expensive) cities. Not without interventions creating costs or inconveniences actually relevant to the homeless as a proportional deterrent. I'm not sure if that's even possible without being cruel though.