Because stingrays don't have a legion of air-breathing symbionts inside them?
In seriousness, all fish have a "crush depth", too. For most fish, their swim bladders physically prevent them from swimming too deep, and for most deep-ocean species the bladder would rupture if they swim too shallow. Rays don't have swim bladders, which can give some species a much wider depth range than their non-cartilaginous counterparts, but nevertheless they could not function properly if placed way outside of their natural depth zone.
Stingrays are for the most part shallow-water critters; though there are some deep-ocean species as well; even these are limited to the mid continental slopes. You won't find them out on the abyssal plains.
