[hncomment]

most sprays are gentle

If you say so. Last spray setup I saw was a garden hose with a pistol-nozzle at the end (in Indonesia, no paper provided). Even assuming some other more-gentle delivery mechanism, the geometries make it seem likely some of the 'rinse' will drip back onto the nozzle, higher areas of the toiler, and other parts of the lower body. Paper allows precision.

check with your hand

Yuck! Even though hands get a wash later, the paper approach has as its goal: hand never contacts feces, toilet/black water, or rectum area.

•leaving dried fecal matter in your rectum*

If you're wiping fresh feces with proper paper, there isn't any visible fecal matter when finished.

Perhaps there's trace residue below visual perception. If so, it's not obvious that a gentle rinse with water alone would be any better at removing/sterilizing that. (A powerful rinse might help: but we've ruled that out to prevent splatter. A rinse with soapy water might help: but that doesn't seem to be the standard. Extra physical wiping with damp tissue might help, so that's sometimes done if there's a fresh-water source within reach.)