Why Do Some Adult Fantasy Books Get Labelled as YA?

Why Do Some Adult Fantasy Books Get Labelled as YA?

I've been wanting to make a post like this for a loooong time and I've definitely vented about it on Twitter before, but I finally did some research and got some very loose evidence to show what I'm talking about. The question I'm trying to answer today is: why do some adult fantasy books consistently get wrongly categorized as young adult?