The company says: "We help programmers find great jobs at Y Combinator startups." What's so great in Y Combinator startups? I mean why do they narrow only to s

The company says: "We help programmers find great jobs at Y Combinator startups." What's so great in Y Combinator startups? I mean why do they narrow only to such startups? Wouldn't it be better to just say they help with finding jobs in startups?