I feel like a different team working on a different game, with a different story, in a radically different game engine, based on a radically different D&D ruleset, twenty years later for a different company, has the right to make different casting decisions.
Basically at this point if you are trying to sell a D&D videogame that's going to involve voice acting not trying to hire one or more Critical Role performers (if you have the means) is basically publicity malpractice. They are not only professional voice actors who bring special D&D cred, but will then promote the game on their show viewed heavily by the target demographics of the game. As for why they chose to give him the role that supplanted another famous voice actor, it's probably because it is the highest profile role in the game that could be recorded in one session or whatever.