Soaking up the game from Kevin Nash and Shawn Michaels more than anything turned him into a ruthless politician. I also think certain people surpassing him and becoming huge stars in the process on multiple occasions when it was supposed to be "his time" got to him.
He was supposed to win KOTR '96 and begin his push up the card, but the MSG incident happened, he was punished for it and Austin seized the opportunity and it was the beginning of him becoming a superstar.
So HHH recovers, wins the IC title and has Mr. Perfect as his manager. Instead Perfect leaves for WCW and they give the IC Title to a green newcomer named Rocky Maivia.
But hey, at least he has Chyna as his bodyguard, and they give him the legendary Mick Foley to feud with. He even gets to tweak his character and create a stable with his buddy HBK. And when HBK gets injured and semi-retires, he takes over as the leader of this hot stable. The only problem is that he still seems somewhat nondescript and he goes down with an injury when he wins the IC title for the second time. What's more, Austin is a huge superstar now, crossing over into the mainstream, and Rocky has tweaked his character and is a step ahead of HHH, mainly because he's drastically improved and the fans are starting to really like him. He becomes so good and the fans like him so much, in fact, that he gets bumped up to main event status and becomes World Champion. All while you're sitting home injured with a bum knee.
Several months later, he finally gets his big megapush and his transition to main event status begins. He's just starting out when a fresh young newcomer named Chris Jericho comes to the WWF from WCW, causing a big stir, big enough to threaten your spot and what heat he's been able to build. Or so he thinks. So he finds ways to bury him and make him less of a threat to himself and in the eyes of the fans. It's really from that point that he would ruthlessly politic against anyone whom he deemed a threat to his rising status as a top star. Pretty much any reasonably big name from 1999 onwards was a victim. He had the power long before, and the protection, but getting involved with Stephanie both onscreen and off only solidified his protection, his power, and his main event status (I'm not saying that I think he doesn't legitimately love Stephanie
).
Just my theory.