I noticed in East Asia, they also have some tendency to have floor to ceiling windows through the whole bathroom to the bedroom, sometimes with no curtain either. I am not sure who this is for

The legend is that if you invite a lady for the night, it's so you and she can keep an eye on each other, in case either is worried about one going through their stuff/wallet while the other is in the bathroom.

I stayed in such a hotel, and getting up to go the bathroom I noticed someone had flicked a business-card-sized advertisement under the door, for said companionship...

I've seen that in japan, but they had a switch that would electronically switch off the window (it would become opaque white).