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?
Celebrities don’t always cost much, you have to remember that those high rates they get paid are optional, there’s a base pay for actors, and they can take that rather than their typical high pay if’n they want. Throw in that in a lot of ways voice acting is easier (no costumes, make up, no standing around for a scene to be set up, etc), and it’s effectively a quick and easy buck for actors.