Dumb question, why do “sensitive” spots on the body need more nerves? Couldn’t you just have the normal touch-sensing nerves and map signals from specific spots on the body to stronger/pleasurable qualia in the brain?

Having more independent samples helps filter out noise. If you had individual sensory neurons with outsized influence, then misfiring of such neurons would also have outsized influence.

This makes a lot of sense, thx!

Sounds plausible at least, but I think the question isn't necessarily making a valid assumption. Why do men have to have nipples? Why is our retina installed backwards? Why do sinuses drain upwards? It's just a path evolution took, it doesn't jump to some optimal design.