i grew up watching the animated cartoon of fonz and the happy days gang but i wonder how come the cartoon did not feature the the entire cast, i wonder how potsie, chachi, joannie and the rest of the gang would have looked in animation fourm

I am also wondering why The Rest of The Happy Day's Cast was on
The Saturday Morning Cartoon The only one from The Happy Day's Cast
who was on The Saturday Morning Cartoon was Ron Howard.

THE FONZ & THE HAPPY DAYS GANG did feature the voices of three members of the original series cast: Henry Winkler (Fonz), Ron Howard (Richie) and Donny Most (Ralph). They were joined by Didi Conn (Cupcake) and Frank Welker (as the dog Mr. Cool). It would have been pointless to reconstruct the entire cast again. That had already been done in live-action. Thus, Hanna-
Barbera added the traveling-through-space storyline and some new characters.

H & B also took a different approach with LAVERNE & SHIRLEY. The animated
version only featured Penny Marshall (Laverne) and Cindy Williams (Shirley).
But Williams was only involved the first season. The format had Laverne
and Shirley in the Army (with Ron Palillo as Squeely, a pig). After one season,
the show's title was changed to LAVERNE & SHIRLEY WITH THE FONZ, and
Henry Winkler reprised his role as the Fonz (bringing along Frank Welker as
Mr. Cool). But Michael McKean (Lenny) and David Lander (Squiggy) were
absent from both LAVERNE & SHIRLEY cartoon shows. (Trivia note: Michael
McKean and David Lander did, however, reunite as voices in a Disney TV
cartoon series, based on the movie "101 Dalmatians." But I digress.)