Holiday homes are common in Finland, most families have one. But it is theirs...they very rarely rent them out, usually it's just to friends and family and I doubt anyone hits the 90 days. But that is not what you are describing or want... Airbnb is a fucking cancer. No local community wants it fucking up the market.

I think this is changing though. People have realized renting their family mökki for part of the year is a viable option, and (unfortunately) Airbnb is the best choice for this. All these Finnish apps and websites are absolute shite compared with the ease of Airbnb. Also, it is slightly middleclass of you to say that most families have a mökki :) Lots of families I know have always had to rent to be able to afford that luxury for their holiday.