Because no matter what AJ's crimes, they came AFTER the trilogy of Suck declared war on him.
And they have always been far worse human beings than AJ. And they've done far more damage to Michael than AJ could have dreamed of doing.
And it's absolutely hilarious that AJ's biggest crime was being an alcoholic. A recovering one at that.
While Sonny and Jason were unrepentant murderers, kidnappers, racketeers, who lived and breathed to deliver misery to Port Charles on a daily basis.
But AJ had to be the saint? AJ had to be worthy?
No.
AJ was the father. That's why he gets to be Michael's father. He didn't have to steal Michael to be a part of his life like Sonny and Jason did.