What if everyone wants their free housing in Helsinki? California's problem isn't a lack of homes per se, it's a lack of homes where people want to live. (San Francisco also has a massive drug-use enforcement problem.)
What works for Finland might not for California without us acknowledging that every homeless person who wants housing in San Francisco isn’t entitled to it. They can be entitled to housing. But not where they want it.
Finland is a bitterly cold country (in winter) with a hard to understand language and 5 million people. The local homelessness problem has some relatively low upper limit.
The US is a country of over 300 million and SF has very good weather all year round. Its migration potential is almost two orders of magnitude bigger.. If you simply give a home to everyone who turns up in SF and says that they need it, you won't have enough homes. You could deny coverage to anyone who moves to SF after a certain date; that would mitigate the "amount of homes needed" problem, but it remains to be seen if the homeless community does not grow back to its original size.
Source? (Curious for their definition of vacancy.)
A cursory glance shows many of those homes are being renovated or sold [1]. The pied-à-terre / vacancy tax isn’t a terrible idea, but it’s a band-aid on a missing limb. (Though further penalising housing development seems like a very San Francisco way to compound the problem.)
[1] https://www.sfexaminer.com/news/housing/san-francisco-saw-bi...