I doubt there is any truth to it being an ego game unless Verizon is insisting on including some kind of unremovable bloatware that Microsoft is saying no to which doesn't make any sense since they greenlit the HTC M8.
Otherwise, what does Verizon or Microsoft gain? Nothing. Why are they saying next to nothing? Really hard to say, but my guess is the truth is probably far more logistical than it is political.