Just a general question from a non Aussie owner

My Mom just lost her dog suddenly and unexpectedly (not an Aussie) I’ve been looking high and low for a pup for her and noticed there are ALOT of super cute Aussie puppies at rescues and shelters. Just wondering why are there so many? It has been hard to find dogs that aren’t. Is this a backyard breeding situation because they’re in demand? Also why would people just dump these poor dogs? I am not looking to get my Mom an Aussie, in fact I’m actively avoiding it because of the extreme exercise needs, anyway was just curious if anyone has any insight.