It boils down to this: there's only a limited amount of zoos and breeders willing to take the wild burms. When those facilities say "no more" what then? You're still going to have burms left over. Can't ship them back to the native country since they could easily be carrying illnesses/parasites that the native burms don't have a resistance to.
The most humane and cost effective thing to do is euthanize them.