Because it sucked. The UI was nothing earth shattering, in fact it confused a lot of people. The results were short of impressive in terms of relevance and use

Because it sucked. The UI was nothing earth shattering, in fact it confused a lot of people. The results were short of impressive in terms of relevance and usefulness. If you're going to beat Google, you're going to have to be better, easier and faster. Cuil didn't just fall short in all three, it was abysmal in all three.