Nobody knows the reason why the original voice actor for Minscs is not returning, so any assumptions regarding that are pointless and they don't owe telling people why, as any reasons they may or may not have regarding the decision is strictly up to them.
As for acting like it's a huge disrespect for older fans; if I was an older fan I'd be somewhat letdown sure, but also incredibly thrilled knowing that someone who is an actual DnD enthusiast and fan that breathes and lives DnD RPG like Matthew Mercer is replacing a voice actor I enjoyed in the past. Sure it won't be the original, but they did not bring in some random pantsy from the street to do the character. It's the legendary Matthew Mercer, an incredibly talented actor and incredibly nice person. I could not imagine a better actor to bring in.
That to me is quite the opposite of disrespect. To me that's huge respect done to the character by bringing in someone who is actually worthy of the role and deserves it.
People acted the same way when Roger Craig Smith (voice of Ezio Auditore) was announced to be the voice of younger Batman in Arkham Origins instead of the iconic Kevin Conroy, same as Troy Baker instead of Mark Hammil as the Joker. But they both did a phenomenal work and brought justice to both characters, by bringing in some of their own and remaining faithful to the iconic actors. So I'm sure Matthew will do a phenomenal work bringing the character to life. I jumped out of my seat when I saw him during the Panel From Hell.
