But mathematics notation needs to be extremely succinct because the notation is not just for reading. When you're working something out you often need to write pages and pages of formulae and diagrams by hand. So using a notation more verbose than absolutely necessary would be unnecessarily painful.
Programming is different because you can use a text editor with copy, paste, autocomplete etc. But I imagine that if I wasn't allowed to use any of those then my variable names would shrink down to one letter when I was programming too.
Also, I think that making formulas smaller makes it easier for the eye to see the whole formula together. This makes it easier to quickly understand the meaning of the formula, at least once you've got used to the notation for that particular area of mathematics.