BR - There are players with egos, and there are players who overestimate their talent, especially when compared to their achievements. The players on this list are in the second group.
Confidence is a big part of the game, and every player that is playing at his best is usually full of confidence.
What do you expect. You tell these guys from their teens how good they are, you tell them they are gonna be a star, you give them ridiculous contracts as 16 year olds and pay them thousands a week before they even need to shave properly.
Let loose with a fortune in the bank as young men with poor guidance, they will run riot and act like kings of the universe and think they have the right to to behave as they like and take what they want as they deserve it- rather than acknowledge how privileged and lucky they are.
This can lead to what you see here.