Can anyone explain why Ayn Rand's ideas aren't considered philosophical? I know there's a lot of bashing her, but I don't actually know what about her ideas disqualifies it as being a philosophy.

I read Atlas Shrugged and aside from it being a capitalistic wet dream, my understanding is her big idea is that people should work hard pretty much for the sake of the work itself. Obviously that's an oversimplification, but I was wondering if anyone had a better explanation.