It's not only the cheap companies. The problem is, most people don't seem to realize just how how much electrical current these numbers actually mean. Several hundred (or even over a thousand) amps is no joke. Whatever theory (besides pure marketing) is behind these absurd C-ratings, I would not trust any of our hobby's batteries (including ports, connectors, cables, etc.) to survive that for anything but the shortest of peaks. Whatever part of the battery might survive continuous currents like these, something else is likely to melt or even vaporize under such high currents over a longer time.

A little example of what high currents can do to smaller metal objects:
https://www.youtube.com/watch?v=xESCXFz8ZQE