GANs were just low hanging fruit that Schmidhuber already found. By most accounts Ian Goodfellow is kind of an asshole, and there was some drama about him a few times over the years. I don’t know the man, that’s just what I’ve heard.
(I like Schmidhuber but I'm not knowledgeable enough to really evaluate his work or claims.)
I don’t fully understand the tendency to do so, but it appears to be fairly widespread.