Many people use descriptive variable names to carry semantic information.
APLers use extremely consistent, stereotypical naming conventions which also carry semantic information. Think "Hungarian Notation" except it's just the prefix part. With consistently applied terse names, the same idea will result in the same code. Easier to visually pattern-match.
It's also worth considering that longer names are not necessarily more meaningful. It's pretty common for everyday programmers to use single letters for something like a loop induction variable. Sometimes longer is just... longer. Consider these three semantically identical K definitions:
a:{x*x}
b:{[n]n*n}
c:{[number]number*number}