I'm guilty of making adoptables, but I don't do pallet swaps. I feel like how the Character stands or what facial expression they have also adds to the Character.
Right now I'm doing a "pay what you want batch", where they could pay the base price and get what they see, or they could pay more and I'd do more as well (make a ref sheet, do a Solo shot or icon etc). Hell in this batch, there isn't even multiple of one species, and an example is: one of them is a feral ice cream Cerberus, the other is a secretary bird (My point is, none of them look alike).
I have personal reasons too... I don't want to take commissions yet, but with adoptables, I can at least give something I already have.
Also some people are indecisive about creating Characters. Someone came to me and told me they turned a design they got from me into their fursona, and honestly, I'm honored I could help.
Sorry for the rant, but I do agree taking someone else's base, and making five recolors of it to sell is kinda.... Poor taste
Tl;Dr I like to make and see unique adoptables, because when done right they look awesome. Color swapping is eh :/