No More Ladybugs?!

So you would think that after releasing almost 2000 ladybugs near my rose bushes, that I'd be able to find at least one on them right?! Well, I can. Just 1. Seriously, I can only see one ladybug around. Do they not like the juicy aphids feasting on my roses? I spent $10 on a bunch of bugs and they just disappeared. Grr. Stupid bugs.