There are many differences between the practice of mathematics and programming, to the point that I do t believe that they are comparable.
One basic thing is that PI (and even more so E) are pure abstractions. They correspond to certain physical or intuitive concepts in certain contexts, but their identity across contexts is more important. Even in programming, we sometimes use one-letter variable for very abstract things (the loop variables i, j, k; T, U, V as type arguments in C++ and co, or a, b, c in Haskell; and probably others).
Another major difference is the way this is actually done. Programs are written once and then mostly read, tweaked, debugged. Mathematics is all about writing and writing and writing, a lot of times from scratch. You're not as Lilly to be editing a file from 2 years ago, you're more likely to be writing a new attempt from scratch. And, people will likely only read your final version, not your hundreds of attempts before. So efficiency in writing your ideas is all the more important than in coding.
Another aspect is that, a lot of the time, the mathematician will spell out a lot of intermediate steps between a problem and a solution that, in a computer program, actually fall in the execution, since we're not in the habit of proving our code reaches the final state we envision (even informally); and certainly not in-line with the rest of the program. So again, in mathematics you end up writing a lot more the same few symbols, making long words all the more harmful.
Imagine
X + 6 = 5X
X - 5X = -6
-4X = -6
X = 6 / 4
Spelled out as
Unkown plus 6 is equal to 5 times Unknown
Unknown minus 5 times Unknown is equal to negative 6
Negative 4 times Unknown is equal to negative 6
Unknown is equal to 4 divided by 6
Which of these is clearer and easier to follow?
Edit: I'll also add that function notation works great for unary and maybe binary functions (though operator notation is generally nicer for binary functions), but it becomes horrible for anything past that. For example, the sigma notation for sums is much easier to remember than if I wrote `sum(1, 789, some_value squared)`.