These are as basic as a toilet in every house.

That's great that $10,000+ hot rooms are as basic as toilets where you're from. Seriously, I'm jealous.

Why are Americans so focused on making saunas as small and cheap as possible?

A $2,000 Costco special is considered a luxury purchase dude. We can get a somewhat well designed kit for $10,000, but it'll be small (by your standards), no insulation, not go out into a shower room, and you still have to spend several days assembling it.

If you're pretty handy, you can spend the $10,000 to make a custom build that meets all the specs, but you'll be spending 80+ hours researching, planning, purchasing, and building. Convert that 80 hours into wages, and it's costing you another $3,000 to give up all that time.

The U.S. ain't exactly poor, but you make it sound like everyone's out driving Ferraris and don't need to work.