And worked on humans. There'd be no need for dating. All you have to do is LOOK at someone and you are together for the rest of your lives. How much easier would life be! If you're starting to get lonely just go on a database or something of everyone in the world and BAM you've found your soulmate!
I think that would take the fun and satisfaction out of it. Plus, it honestly seems a little sketchy. What if you imprinted on someone on the other side of the world and had no way to get to them? What if you imprinted on someone of the opposite sexual orientation? What if you imprinted on a family member? What if you pulled a Jacob and wound up imprinting on a BABY?
That would make love cheap and not worth it. Working at relationships is what gives them value. Imprinting is a stupid cop-out invented by Meyer to get out of writing detailed, in-depth relationships between characters.