The article [0] I read is in Finnish and now behind a paywall, but it explains that a woman more or less out of her good heart allowed someone to stay in her flat for a time while she was on an assignment in another country. The person staying in the apartment never really paid any rent, but became a "tenant" so that it is impossible to evict her. The owner has to refurbish and fix the apartment at her own cost, while the person staying there is protected by law and lives there and pays nothing. And makes a horrible mess which the owner has to pay.
It is obvious that such examples send a very strong message: if you're away for a year or two, DON'T give your apartment to let. Keep it empty. If you plan never to use it, then sell it. But if you intent to come back it, just keep it empty. Everything else is too risky, due to the regulations.
Then it's now fashionable to frame this as a xenophobic "rich foreigners come and hoard our apartments and cause housing shortage". The actually guilty to the shortage is local, populist regulation.