It’s as has been mentioned for two or three reasons:
1) the narrrarive created by successive England managers. Let’s be clear the number of united players abandoned, shit on, or plain ignored by England during our period of success was ridiculous. Favouring older, players, London clubs and Liverpool caused some of this. Any excuse was trotted out and Hoddle was one of the worst. Plenty of players have said that if you turned Hoddle down, or he didn’t like you for any reason you could not get in any of his teams.
2) media narrative was similar, as has been the case for a long time, and still is, the media is full of Liverpool and London centric journalists. They loved running down Cole even during that 99 season.
3) he didn’t give bombastic interviews or cosy up to the press. He treated them like they were shit, I think due to how they treated him
4) other fans bought into it, he was a united player and very few got any respect. Look at how most other fans talk about any of our top players (scholes, beckham, Keane, ferdinand, Neville), all skated by opposition fans.