Variable names are usually idiomatic within a field/carry some semantics. e.g. k is angular wavenumber, omega is angular frequency. r is displacement. etc. They just use short names to prevent the name from distracting from the shape of the equations it's used in, so that it's easier to say things like "this behaves like a transport equation but with a source term that's proportional to the strength of the Foo field squared" or whatever.
Lots of phenomena have very similar governing equations, so downplaying the names of variables in favor of the structure/context they're used in allows for efficient transfer of intuition.