But I remember one of Tesla-Björns earlier videos where he and his pal Jörgen turned the Millennium Falcon into a sauna using the cabin heater and posing more or less undressed. So a lack of sauna can't be the reason, unless Finns find it lacking. Which is of course a distinct possibility. Anyway, one contrary factual argument.
OK, in the absence of posts purporting to be from Finnish people, I will just throw in a random (and confirmed several times) anecdote:
Q: Why is Vodka in Finland sold in 50cl bottles, as opposed to 70cl ones?
A: Because you drink one bottle every day, so 70cl would be too much.
PS. Also, Finland is the country that gave is Linus Torvalds, thus Linux, the Operating System of the Tesla.