[Iargwath]

That is a fair question the guy who be short. But you must remember that it is a Dwarvish belief (so it is hard to determine if it is indeed fact). The best thing i could come up with as an answer was this:
One of the srongest characteristcs of the dwarves, was indeed the ability to craft. It would be moral for them to help Aule (their creator)to re build Arda for they already derive many skills in craft from him. It could also be part of their fate...who knows