>>718575382
It comes from Sakurai wanting the Kirby anime to stay in his own world, so he mandated against the anime creators doing that "mascot befriends human children and the show happens through them", sort of like the Doraemon format. But then they ended up doing that anyway, they just made them humanoid alien children instead.
And Sakurai has no problems with humans in Kirby, he made Nightmare and wanted to let people believe the NME Salesman was a human for most of the series.
My personal theory is he hates Adeleine not because she's human in itself, but because the way she scales to him means Kirby is probably almost 3 ft tall, when Sakurai is very attached to his "Kirby is 8 inches" headcanon.