Was because you were downplaying the importance of the rag. The rag is more important than the water is. If you’re cleaning a mess, and your choice is between water and rag, you choose the rag.
How commonly do bidet users scrub with both TP and water in a single sitting? The internet and this comment section suggests it’s pretty rare.
People are choosing between bidet (water) and tp (rag), and in your analogy, you’re saying the sensible choice is to wash something with only water and no rag. Your analogy only holds water (lol) if you don’t actually think about it.