"Why are they disputing over it? Any ideas?"
My best guess would be "Cryonic suspension". He probably is right next to the headless Ted Williams or it could be Michael wanted to save the DNA and Satan wanted no part of another Moses. Just a guess.
Well....that's as good as anything I have ever heard.
We know that of the two, (Satan and Michael), Michael is the stronger. [Revelation 12:7-9] And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels and prevailed not; neither was their place found any more in heaven. And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.
It's one of those verses that seem to go down a rabbit trail and disappear. [Jude 1:9]