They don't, but if it happens with a few ICOs people won't trust ICOs anymore and these kinds of scams won't repeat much.
Anyway, has there been any verified ICO scams yet? Seems to me like it's not much different from startups promising BS/bad ideas to gullible VCs who end up losing millions. In this case, ICOs are selling these ideas to the little guy through crowd funding which is different but the little guy usually invest a few bucks in these ICOs so if the ICO fails to delivers it's not as big a deal unless one invests his/her life's saving in said ICO but then that's a pretty risky idea one needs to take responsibility for.