Well, why shouldn't they? If he's making more money in the UK why should he go to the USA before the money is there?
A similar situation would be with Joe calzaghe, he was dissed for years about not fighting Americans, then you sent one over...
My point is by the time Naz fought in the USA he was done, he had no interest in fighting, he ditched his trainer, the guy he'd been with since he was 9 years old, had his brothers running everything and genuinely believed he had the game nailed down and could beat anyone because they couldn't do what he could, so he stopped training, stopped sparring, just lived it up and jumped over the ropes when it was time and still beat Kelley who was no joke.
Then you have Calzaghe, listened to his trainer/dad, respected the game, understood what you put in you get out and retired undefeated.
Now as Americans you're gonna say he beat no one till the end of his career and was just fighting euro bums.
The European boxing game in the 90's was incredible and as a Brit I loved it, I watched the odd USA fight and it was cool but we really didn't need you guys, we had fucking incredible wars, rivalries, upsets, personalities, it was a great time to be a boxing fan over here just as I'm sure it was for you over there.
And no, America wasn't better, or worse, national pride in others achievements is bullshit.