Despair

Well, she has done work in more well known shows than the rest, and she does voice the mainest of the mane 6, so it stands to reason that she gets the most attention.

Would anyone even care who she was if she didn't do a voice for MLP:FiM?

Would anyone care about Mark Hamill if he wasn't Luke Skywalker?

I'm just saying, it's not her fault she has a lot of fans, she's a talented voice actor who has voiced a lot of things. I think it's just that none of her other work has ever had a fanbase on the scale of MLPFiM, so she wouldn't have gotten the same widespread attention she does now.