No love for $x, $y, or $z?

In those cases, at least, there are some longstanding traditions that impart meaning to those names. Break those traditions at your own peril, but if you use them within the proper context, that's not a bad thing at all. The same applies to $i and $j.

Not when they're used in every context.

Well, yes, but I already covered that: if the names don't fit within the tradition that imparts meaning to them, then you need more descriptive names.