i and j etc is bad though, but for a different reason than usually claimed. it's suboptimal because it's hard to search for. just use ii, jj, kk, etc
One letter variables are supposed to be used in scopes that fit on the screen completely. You might as well search for "for"
TL; DR: it's on purpose.
Exactly, and ideally in less space than that. If you have something like:
for (i=0; i<10; i++) {
foo(i);
bar(i);
}