Earlier quoted context omitted.
Superficial take IMO. Don’t need a selective pressure for a cognitive process to work in a particular way. You just need a selective pressure for the cognitive skill and for the way that skill works to at least not have a pressure against it, biology being full of engineering compromises. Learning well with handwriting, IMO, has little to do with hands specifically, but memory and understanding in general, where the…
My guess/impression is that the act of writing something down passes the information through different parts of the brain, and then you have two independent memories of the facts.
(I did mention in my other post I can sort of see why handwriting is a movement more akin to other ways we manipulate the physical environment - but in fact I use the "swipe" style keyboard entry on my phone, which is surely not that dissimilar - using my finger to draw shapes. Touch typing is certainly very different and hard to correlate with other actions we need to perform in the real world, in some ways it's surprising we're able to become so competent at it, though obviously our ability to make finely tuned manipulations with our fingers is a huge part of our evolutionary success).