Earlier quoted context omitted.
Because it makes people look like pathetic muppets. If you mean "Fuck Joe Biden", say "Fuck Joe Biden", don't clutch your damn pearls about it.
When the majority uses vulgarities, how does not using vulgarity make one a muppet? I’d also consider the Muppets rather avant-garde for their time, so maybe you mean it as a complement as in Gonzo, Fozzy, or Beaker (or any other pathetic Muppet).
That said, I am perhaps guilty of the same offence there - per the BBC America article "10 British Insults Americans Won't Understand" [1], a muppet is "someone who’s stupid, gullible and incapable of independent thought" - unfortunately the pearl clutching tends to extend to the typical four letter word I would use for such people.
[1]: https://www.bbcamerica.com/blogs/10-british-insults-american...