Considering that US houses usually either have a crawl space, basement, or are on a slab the lack of a drain is weird when you think about it. You would think wet locations would be required to have a drain.

I think a lot of European houses have floor drains in the bath, you can basically hose the bathroom down.

More on topic. Outside of the US R290 (propane) heat pumps are common. But illegal in the US because the refrigerant manufacturers control the code bodies. You can have a 20lb propane tank hanging off a BBQ which in normal operation is literally on fire. But you can't have an R290 monoblack cause it's too dangerous.