Mike has been integral in several other great projects and I think he just likes to be diverse. He really likes working with Neal Morse. He's been on most of his albums, did Yellow Matter Custard, Transatlantic (which has been hugely successful). He's also done O.S.I., Liquid Tension Experiment, Avenge Sevenfold, Hammer of the Gods, and Amazing Journey as well. I feel like Mike just wants to see what else he can accomplish. After all, he's the youngest drummer inducted into the Hall of Fame.
Maybe he'll show up on the next Flower Kings album too. Who knows?