You're right about the ego thing.
It's easier to become a live act allowing them to have minimum interaction while still making lots of money. There's no money in record sales any more so why go through the hassle of being in the studio with people you hate? After 5 years on the road playing massive stadiums they have enough cash in their accounts to not even have to be in one another's eyesight. Ian banging his drum over Reni's last solo / intro at Hampden summed it all up. The drummer's a cunt (not even "Reni", but the "drummer") showed the cracks had appeared as early as Amsterdam.
He might be a cunt but jump to 1:55 below.
Together with Brown, that cunt is the Stone Roses. One's the heart, the other's the soul.