It's not about saving a few bucks on a door. It's about discouraging you and your friends from sharing a single room. Hotel sees the money they're leaving on the table and will trade you for it for the low price of watching your buddies do their business.
ChrisArchitect•48m ago
What happened to bathroom doors? [video]
https://www.youtube.com/watch?v=QFPGUTyo9Yk
(https://news.ycombinator.com/item?id=46062242)