[brobdingnagians]

If you work with them long enough it becomes second nature to read them, and then it is easier to manipulate and compose them. The rest of the context is the background knowledge to understand the pithy core equations. Papers are for explaining concepts, equations are for symbolic manipulation. Meaningful variable names would be middle ground and not good at either, except to help someone not familiar with the subject to understand the equation, but a lot of the symbols are so abstract that they really need to be explained in more detail elsewhere or would be arbitrarily named.

[np_tedious]

If you're in an abstract/general mathematical function, then sure: single letters. If you're doing more business logic kind of stuff (iterating through a list of db/orm objects or processing a request body) then the names should be longer

[flqn]

Mathematics doesn't usually deal with databases or http requests