For the same reason why there is so many OC alicorns.
Because people want "awesome" OC's.

I had an OC alicorn that was raped and cut up add a child and has his wings cut off so does that still count ass a shitty alicorn OC?

Me
But he can't even magic and never gets his cute mark

Well then he's a cutie markless, previously been alicorn

Yep
Better than most alicorns

You see, this is why I hate OC's
They always think their better, even though they've never even been seen on mlp.
Or had any relation to anything they have every done.

Because everyone is shallow and unoriginal