Apart from his clear love for the club and fans, I wonder if his decision is also because he now smells blood. He's slowly been working his magic on every aspect of the club, culminating in a team of mentality giants who can beat anyone and who've taken 73 points from the last 75 available.
He knows his formula and template works, just as it did at Mainz and Dortmund. He knows he has owners and staff that are all on the same page with one vision.
He also knows that not only are Spurs, Arsenal, Utd, and Chelsea still in transition, but that City are starting to stumble - their players and manager looking vulnerable and lacking that aura of invincibility. He knows that City are reliant on a core of ageing players, and that Guardiola might not stick around for the rebuilding job.
I think he knows there's an opportunity with this squad to dominate for 3-5 years whilst the others play catch up and City wrestle with the concept of being mere mortals. I think the Champions League win and 97 points silenced any critics and was a big weight off his (and the club's) shoulders, and that parade will have reminded him of just how much it all means. It's also classic Jurgen to announce the news when he knows Merseyside is feeling low, and the way he delivered that message was like he was talking to every fan individually.
What a time to be a red.