They do invest because they do believe in the project or became interested in it. Otherwise, they'll ignore it and move into an ICO that fits their interest. Others invest and hope one day that luck will be on their side to gain profit. I don't really see an ICO nowadays who has truly potential, unlike before where ICO's has really their own purpose. I was glad that I benefited from these kind of ICO's (won't name them) but I did really gained some profit in it. I do hope one day devs will change how the game was being played today and become more strict in choosing participants especially in airdrops where will it create such hype and be dead at the end.