Maybe the like them but want to have them for a very low price. I stopped doing adoptables because people were asking me to offer them, because they were always asking for such low prices that it was a gift in the end. However I think an artist who think of a design for a character doesn't have to give it for almost nothing. I think 5$ for your adoptables like these
[link] is a really good price. And bigger ones, with more details and sweet colouring could be at 10 or 15, so the price you give if I remember well. I think that it is quite fair. But if people don't buy them easily that's maybe because they are humanoids or simply because you did a lot of them already and they don't want that kid of adoptables anymore. I don't really know. I sold kemonomimi adoptables, felines, they were bought the day I posted them. Then I did a new set of three kemonomimi cats, they were also bought the day I posted them, then I tried nagas, same, and then cecaelias, but these were not as much appreciated as the kemonomimi. Then I tried new ones but nobody wanted to buy them, maybe because they were getting tired of them. §It's what I told to myself, so I stopped proposing adoptables since nobody wanted to buy them. I had comments like "they are cute ! I wish I had money..." But nobody bought them. And that's the kind of comment that annoy me a bit. Thank you to say they are cute, but I don't want you to find them cute, I want you to want to have them and buy them... ^.^
Anyway, maybe you should try different adoptables with lower prices at the beginning and then propose higher prices. Maybe than could work. Or simply, wait a bit before doing new adoptbles and when you come back with some new ones in a month for example, people will easily buy them. Putting too many at once is also like this people will stop buying them I think. But that's only my opinion. ^.^
I wish you good luck with your adoptables though !!