Think of the fact that by raising you isolate yourself and you're not going to get called by many people unless your table is loose, which means that you're probably playing against someone holding high cards like A-K, A-Q, A-J (there's the possibility that you're playing some donk and he called you with Q-J, K-Q, K-J aswell).

That means you have a made hand and if no high card hits the flop you can try (and most of the time succesfully) taking the pot right there (considering you didnt hit your set).