This is probably due to jumping on the very tail end of an oversaturated meme that already has at least one firmly established web tool. Roflbot's interface is also somewhat confusing, and was even worse when it had its highest exposure via stumbleupon.
That said, there have been some high points. Several lj communities have discovered roflbot and are making amusing stuff.
If you like roflbot and think more people should check it out, won't you spread the word? Do it for the cats.