In case of math literature, I'd say it is mainly because the equations would be horribly long.
Things like integral computation comes with lots of details, or some kind of long exact sequence. Experts would have trouble understanding it, while normal people almost certainly have no interest in understanding the formulae.
Also, often there is no meaning to the variable. Like, in a real function f(x), x is just "a real variable". There is no additional meaning to it.
As for other fields, I dunno. They might have copied math literature style or something.
Formalizing e.g. limit is quite interesting! Limit is related to tendency; sequence x_n converging to x means for large enough n, x_n is sufficiently close to x. That is, you can choose N such that | x_n - x | < eps for n >= N. In some sense, you are concretely defining what rough terms mean!
To look into these, you can read through books disregarding proofs. While proofs do hold ideas, they can be headache-inducing.
But that's from twitter (or "X" shudders), and how do we know it is a real original?