Hahaha, that might be one way to think about it.
As I've seen it, it's a way to get art from one of the artists you like, while at the same time getting a new character whose design is complete, and can be fiddled around with.
For the artist, it might just be something that's faster than commissions, or sometimes a character of your own you're not going to use. There are probably plenty of other reasons though.

most artists use templates they colour digitally. others draw a new critter for every design. sometimes a fellow artist would purchase an adoptable design that catches their eye and fancy. happened to me, so. :)

It's something that poor artists do to get rich people who seem to have nothing else to do with their money to pay the artist to be creative for them.It's like a normal commission but one step further toward the artist doing absolutely everything.

It doesn't necessarily mean someone is no good at designing things themselves, though I am sure there are folks that do use it that way. I have seen mostly the copy+paste boring variety, but occasionally a good artist will make adoptables with a pleasing aesthetics and original art. I think I have even seen one or two that I might buy [but also that quickly rocketed out of a range I could afford], even. I am perfectly capable of designing a character myself, but it's not like nobody has ever thought "what a cool character!" about somebody else's. So it can function as an extension of that, in my eyes - you see something someone else designed and you like it and have the opportunity to own it in a completely legitimate way.

I will admit that it does seem to get used in such a way that it is often boring - using the same line art and just going crazy with designs, but eh. Shrug. I am not going to throw hate on the people who do that or the people who buy it. Do we hate on people who commission logos from artists? No. Artists usually have a better eye for design [hopefully] so it's reasonable that someone might prefer to have something designed for them, or buy something pre-made. I mean, how many eye-sore characters are there? Not everyone grasps the elements of design as well as others, so, those people have a fortunate choice these days with the advent of "adoptables".