The way I saw it and how I remember it.
BTS never had more opportunities than EXO before the BBMAs.
Sure, SM never pushed for Western promotions and if anything they didn't take advantage of some opportunities that were given to them. I think it had more likely to do with their past failerd endeavors to promote one of their groups in the US that they thought focusing on Asia was better. They couldn't have predicted the China ban of kpop.
But the thing that made the most difference was the way both fandoms dealt with the whole issue.
I have said again that Exols showed big stubbornness when it came to Western recognition. They thought that it wasn't something that was feasible, it was a waste of time and kpop only needs Asia.
Whereas, Armys never stopped trying to find new ways to promote BTS to everyone who would listen.
When the kpop community was laughing at the Western Validation thing, Armys promoted BTS music left and right.
And when people saw great music, great performances and great personalities, they stayed.