I’ve read that one reason could be due to prostitution during WWI / WWII.
Americans saw bidets over in Europe during the war, mainly at brothels, which gave them the idea they were unclean, non-Christian, idk. Maybe if you said you liked bidets then everyone knew you had been to a brothel.
I didn’t fact check it. Doesn’t really matter - I’m taking a poop right now and I’m about to blast the poop away with my Toto. Eat this pleasant, warm water, turd balls.