A screen is built to move you along. There is always a next tab, a notification, a place the eye can go. A page does none of that. It sits still and asks only that you keep making marks, and the making is slow enough to let a thought finish.
Writing by hand is not better because it is old. It is useful because it is unhurried, and because the hand keeps pace with a sentence rather than racing ahead of it. Things you did not know you thought tend to surface in that gap.
None of this requires neat handwriting or a special notebook. A pen and a plain page will do. The point is not the object; it is the particular quality of attention a page still asks for, and a screen rarely does.