Because voice acting is more than just reading lines and doing a voice. He was a great performer of those characters. Basically the essence, the cadence, all that, as if Matt Stone/Trey Parker were replaced on South Park. Much improvisation was behind the voices as well which is where a lot of the offbeat performances came from. Just need to watch this …
More importantly, it’s forever tainted now. I understand Adult Swim wanting to continue cause of $$, but just because Roiland is fired creatively, he’ll still be profiting from any future seasons as creator. I’m sure his people made sure of that in his contract.
IMO, finish Rick and Morty, and do a spin-off in that world (it’s endless) and keep the talented writers, animators, voice actors employed without having to put future money in this pos’s pockets.