It's not just momentum. "Non-obvious" is relative. Every mathematical paper is built on top of thousands of pieces of foundational work, how do you pick which pieces of the foundation are obvious and which are non-obvious? And how do we even use descriptive names? Descriptive names were used in older works like Philosophiæ Naturalis Principia Mathematica which are practically unreadable (even when translated into your native language) compared to more modern ways of writing things like "F=ma", "F=mx''", or "F=m d^2x/dt^2", which are fantastic to understand. Or if I'm writing something like "x+0=x", is there really some descriptive name I can use for "x"?

Or in short, we tried that and terse notation tends to be both easier to understand and more concise.