I'd say a large part of the difference is better play in marginal situations. Making a tough laydown to save your stack, making a tough call to win a huge pot, making a well timed effective bluff into a large pot when most people wouldn't risk it, etc. Within these key moments, if a player is able to make the correct play significantly more often than the good players, I'd say that would be the difference that makes them great.

Also, I'd say extracting the most possible value out with winning hands, and risking the smallest amount necessary on bluffs. Good but not great players will often scare out lesser hands when they have it, and risk too much of their stack when they bluff.

Most of the things in this thread I'd say more address what makes a player a good player, and not the difference between the good players and the elite players.

But I'm also of the opinion that no one on this board is truly an elite player. There's a world of difference between us and the Phil Ivey's of the world. Anyone that truly believes that the difference is just bankroll related is delusional, in my opinion. There's a reason that the elite players were able to build and sustain those bankrolls over years and years of play.