Gibson's schtick was always to trade on stereotypes. Charitably, his books were "idea novels" about social forces. None of his characters were ever human.
Take one of the protagonists of Count Zero, Marly Krushkhova, "the disgraced former operator of a tiny Paris gallery", who hunts down the maker of the Joseph Cornell-like boxes. She's completely human, and I can't think of any stereotype she would fit in to.
Cyberpunk would have happened without him (Blade Runner was released first), but most things are like that.
He'd also studied English, which helped give him some sensibilities that would appeal to tastemakers. Neuromancer wasn't genre fantasy and it wasn't hard SF. (Even then, the name turned many people off.)
And I guess he won some powerful allies early on in what was then the SF establishment.