In my experience it still comes apart.

I wash with soap when I shower. Do you use soap with your bidet?

Toilet paper doesn't stick when it's not wet. It falls apart when it is wet.

Soap. In the shower I use soap.

This is exactly it.

I used a bidet in Europe in my thirties, and then my ass was all wet. I could dry it with toilet paper and leave bits of toilet paper in my ass hair, or I could dry it with a dedicated ass towel, which is clearly less sanitary than just wiping.

It's wet and uncomfortable, and it's not any better than just wiping. Running a bit of water over something doesn't really clean it anyway.

After a shower you dry off with a towel, obviously.

Do you dry your ass with a towel after using a bidet? An ass towel? Because that's disgusting.

How does having bits of toilet paper stuck to my ass improve the situation?

Bidets are overrated. There, I said it.