I wash my hands because I use my hands to manipulate objects, touch my face and prepare food. Perhaps you perform these tasks with your anus?

If I had a sphincter on my hand with shit inside it, which occasionally farted or shit came out, and washing it would never actually make it hygienic because it’s not a hermetic seal and bacteria from the shit inside would always be on it anyway, then yeah I’d just wipe it with paper. And use the other hand