And then they run out of Latin letters so they switch to Greek. Then they run out of Greek letters so they switch to Hebrew...
You have to remember that math is written for the sake of mathematicians' brains, not for the sake of dumb machines which accept only linear strings of a limited character set through a teletype. A mathematician can look at a formula and subconsciously break it down into constituent parts based on its shape. Multi-letter (word? phrase?) variable names would only serve to add unnecessary clutter and obscure the shape of the formula. Meaningfulness of names is a secondary concern, if it is a concern at all; meaning can be established in the text surrounding the formulas or equations; and if things indeed get too complex for a set of a few formulas, the option is always there to switch representations -- to computer code or pseudocode.
Also, mathematics' naming conventions are quite strict.
The nabla symbol is almost-exclusively used for vector-calculus operations. The letters t, s, u, v are almost-always used for parametrizations. The letters i, j, k, n, m are usually used as indices of summations. We can go on.
There are also Beth numbers (https://en.wikipedia.org/wiki/Beth_number), closely related to Aleph numbers, but as far as I know that is the only place hebrew letters show up in mathematics.
You have to remember that math is written for the sake of mathematicians' brains, not for the sake of dumb machines which accept only linear strings of a limited character set through a teletype. A mathematician can look at a formula and subconsciously break it down into constituent parts based on its shape. Multi-letter (word? phrase?) variable names would only serve to add unnecessary clutter and obscure the shape of the formula. Meaningfulness of names is a secondary concern, if it is a concern at all; meaning can be established in the text surrounding the formulas or equations; and if things indeed get too complex for a set of a few formulas, the option is always there to switch representations -- to computer code or pseudocode.