From an uneducated point of view...
Perhaps they were just breeding for pets. From what I've seen (in my quest to obtain one) they're quite popular as pets and hard to find.
Or perhaps the cat is carrying other genes or traits and the breeder doesn't have a suitable alternative.

It feels a little silly to be comparing cat to mouse breeding but when I was breeding the mices you would quite commonly have to sacrifice the perfect combination to bring in certain traits or genes to your line.
Personally if I were to breed cats I would be a lot more picky but melanistic seem fairly easy to breed out of a line (it might not be, I don't know).
But then if I were to breed bengals I'd end up with a purely melanistic and blue program, so perhaps I'm not the best person to listen to