Sure, but I think we're just talking about two slightly different things here: I was trying to describe the "sociological" reasons why math notation might end u

Sure, but I think we're just talking about two slightly different things here: I was trying to describe the "sociological" reasons why math notation might end up in a state that you don't like rather than trying to list the particular things you might not like about it. I do agree with you that calculus textbooks often go overboard with notations for the derivative, and in fact I remember being taught some (like a capital D with a subscript x) that I then never saw again for the rest of my life. But as to the question of why "mathematicians" would do this, I don't think the answer is all that mysterious: "mathematicians" is a category that includes a lot of different people in different places and there's no central committee that enforces notation standards! It's like that one XKCD comic everyone posts about inventing new standards.