Basically such big names "investing" (helping) surely made a background check and the chance that the investment is good (moon) is somewhat bigger.
But it's a startup after all. And that means that the risk is way above normal.
Even big, established businesses can fail (just remember the social networks from before Facebook). Startups have a way bigger chance for that. And crypto startups...
More than the money the big names bring, it's the reputation.
Bitcoin is not like some company - it needs more than average reputation and credibility, as it aims to replace money.
So the big fish help with that.