@domisotto
Forgive me if this sounds silly, but maybe you're looking at the wrong kinds of publishers. If you're having trouble with people who want something that they can turn into an Extended Universe, then maybe smaller, indie houses, or, short-story publishers would be better. I know there are magazine that want smaller things, though I don't know them off the top of my head.
Even still, keep plugging. It's a numbers game. As disheartening as that sound, keep poking until you get a yes.
@Undertaildoof34
Always! If you're ever feeling down, pop on back, I've got cheesy inspiration quotes for days!