Protheans like to conquer the galaxy and make all other races their slaves. Why clone them?
Well, they'd have a hard time doing that without an industrial base, without any of their fancy technology and without the numbers to really fight anybody - we wouldn't make millions of them after all, we'd just make enough to keep them from going extinct - it would be just sad to let this chance slip by us (their race certainly is interesting IMHO!)
ps: I'd love to have them in Andromeda (but maybe not as one of the ruling species), as it would show we aren't the only ones who thought about fleeing the Reapers (I mean we know that the Protheans came up with a lot of contingency plans - like the stasis-pods and they also tried making the crucible of course (silly plot-device that it is!))