It just feels like it was all of these things at the same time: renewal of the spirit and energies, marketing, ticket sales, James and MP getting along once more, MP recording two albums in a roll at DTs HQ, tour with JP, MP hanging in a DT show... We were all here and witnessed that, it's all there.
It could have gone different ways, though! I for one wasn't sure if even MP wanted to be back, or if the band wanted him back. They could have decided to keep the reconciliation in their side projects and personal life and keep trying it out with DT and MM longer. But it seems like both sides wanted to give this iconic line up a closing chapter, even the final chapter of the band, as Labrie indicated. On that note as well, I highly doubt they'll keep for longer than 10 years. Not for any drama or bad stuff, just because it's also fair these guys retire some time soon! (not that I would desire that at any point, selfishly)