alt Hacker News>your brain is doing more does not mean it's doing the right thing!
the thing it's doing when writing with your hand is fine motor control, one of the most important and distinguishing abilities that humans have.
I tutor in a makerspace and one thing I've observed it's that it's now easier to teach old people how to solder than younger kids, and that in my experience has never been the case before. Due to growing up on impoverished digital interfaces I see lack of dexterity that I've never seen in young people before. Same reason I suspect you see a decline in people picking up tactile musical instruments like the guitar or violin.
I agree that fine motor control is important, I just don't think forcing people (especially kids) to write by hand is necessarily the best way to do it. For example, if the kids went to your makerspace, they could learn fine motor control and probably enjoy themselves more.
Forcing people to handwrite both makes writing more laborious and takes away from what is actually important in writing, which is forming your thoughts. At minimum, when handwriting you can't go back and insert words or rearrange sentences to try out different ideas.
I do still think kids should learn how to write by hand, because it's culturally important. However, I think it could be emphasized somewhat less, and I don't think schools should teach cursive (which, anecdotally, I think is actually having a small resurgence in many schools).