I’ve been going back and watching earlier seasons, which - I thought - had a smaller budget and less recognition. But after taking a closer look at the credits I realized there’s a lot of celebrity heads that are voiced by the actual celebrities. The star trek episode actually had the full original cast - and those weren’t bit parts! I get that the show’s a social commentary, but wouldn’t it have been easier to get sound alikes? Is there a story behind the show’s giant special appearances list?
Also voice work is an easy gig for actors. No need to spend hours in makeup or costume, don’t need to wait around for lighting and whatnot. You can just show up, play around with other actors and then go home again.
With 1/6th gravity, you can work and be lazy at the same time. It’s like being a voice actor!