Who says he shuns DT from his life? Just because he doesn't bring up DT as often as MP does, it doesn't mean that his own opinion on the split isn't out there, if you look for it. He had no problem collaborating with MP on the OSI project ten years ago, either (even though it turned out MP did have a big problem with that). And why would he play on DT's anniversary performances? For us, DT is a big deal; for him, it's likely just a band he played in in his twenties before he even figured out what he actually wanted to do in his life.
Don't get me wrong, if I could live in an alternate reality, it would be one where Kevin found a way to do DT and Chroma Key on the side (because it's not like we ended up getting many Chroma Key/KM solo albums since the split, anyway), or the one where he climbed on stage with DT in 2000 or 2004 or 2014 and did Space-Dye Vest with them. But he doesn't want to and there is no bigger argument behind it. Maybe, if he stayed in the band longer, him and MP would have blown up, due to how opposite their personalities are, but up until 2000 or so, out of all DT members, MP was the one that regularly emailed KM and sent him new DT CDs and stuff like that. It's clear he wanted to keep in touch, and his desires to keep in touch included KM performing with DT on anniversaries and such. KM didn't want to do that a couple of times when he was invited (it's all in the Score drummer DVD commentary, and other sources, I'm not speculating), MP didn't have much fun working with him on OSI either and that was it. But there are no confirmations that they were ever in an argument during the time of the split.