A possible Explanation from Kojima?
Hideo Kojima Excluded David Hayter from the New Metal Gear To Freshen Things Up
Hideo Kojima Excluded David Hayter from the New Metal Gear To Freshen Things Up
Do bear in mind that the character in question is Naked Snake.. aka Big Boss. That's not Solid Snake.
IMO, Kojima is trying to branch the two men apart, identify them as unique characters and not just carbon copies of each other (I know, I know.. but still). Big Boss did have a different voice actor at the end of MGS4, after all, although most people assumed it was because the two Snakes were actually in the same scene talking to each other and it would have gotten way too confusing if both were being voiced by the same actor.
There's also some speculation that Solid Snake will appear in some form in the new game, and he'll still be voiced by David Hayter.