I don't actually know do birds have higher tendency to inbreeding in nature. I know in captivity especially the smaller, more aviary setting kept birds might breed with their siblings and parents if there's not enough unrelated mates.

And with hand-fed bigger parrots getting bonded to humans in general is like grooming, very simplified. Growing up without proper birding tends to cause all sorts of mental problems already, and they might not have any other person or parrot to seek company from, and at worst people do stuff like stroke their backs which is a sexual signal. So what's a hormonal teenager gonna do when the strong instinct of gotta find a mate kicks in?

Edit// forgot words

There's a difference between incest and inbreeding. Opposition to incest, that is sex for pleasure among family members, is a moral position, and apparently unique to humans.

Inbreeding, sex for reproduction, is blocked on a biological level more strongly in some species than others, but it still happens, of course.

In humans, and perhaps other species, there is sometimes sexual disinterest in closely related family members, but this is not "opposition to incest", and certainly is not universal.