To be fair, large corporations buy out the rights to certain characters all the time. Adoptables is just a much smaller scale than this.
Also, I want to say that the whole "adoptables" scene really does seem so retarded to me. I have a mutual who does a TON of adoptables, using the same base too. So she's barely drawing anything actually new, just different colors and maybe changing the ears, but the base is the exact SAME and has been for a few years. And she's selling them for $50+ on average. But hey, congrats to those that can do it I guess.