I’ve never actually watched this particular show, but if it’s anything like American Idol, the audience is already pre-trained to scoff at a certain number of ‘crazies’ who either do ridiculous auditions just to be on T.V., or are truly delusional about their talent and are shown by the networks for the comic relief they provide. So I suspect, when Susan Boyle came out on stage the first thing everybody thought was, “Oh No, here’s another one”.
So, while it’s true she was initially judged on her looks, maybe there was a certain amount of bad expectation already instilled into the audience by the producers of the show.

As an aside, she’s already finding that fame has its drawbacks .