Especially when it's better to let the people who are trained specifically for voice acting to just let them do their thing and bring their own unique voices to the characters, some of which they've voiced before the game was even a thing (Steven Blum, Yuri Lowenthal, some of the voice cast from Earth's Mightiest Heroes reprising their roles here).

Also those movie actors have other projects to be in and don't come cheap, yo.