True. I believe the bathroom is an intervention of the West!
Bathroom and toilet already being built during Mesopotamia civilization.Then the technology passed to other civilization like Indus , Ancient Egypt, Ancient Greek, Roman, Sassanid.
its invention of middle east, from one of the oldest civilization. they already have plumbing and sewage system. the new civilization copied that and improve what have they see. the reason why during dark ages people don't bath because the knowledge is lost, to the west it is. while middle east collected the knowledge from Greek and Roman and improve their current civilization like Baghdad or Andalusia. then when west started rediscovered again what had been lost to them, Renaissance happen, the rebirth and rediscovery of old technology and knowledge.
Then European come to Japan and shared that knowledge. Japanese think bath is japan invention is oxymoron. even Roman take bath in hot springs, long before japanese did.
Japan is island and isolated country. The knowledge they get mostly come from China, even their language actually come from Chinese. Kanji is Chinese words but with different pronunciation. they still write and spelled the same, and have same meaning. their Ramen, their tea, are from China.
apparently, even with internet, they still inside the border of their country and know nothing about other civilization