Ladies & gentlemen, I present unto you people's exhibit A as to why ABC ultimately changed the format for Scooby-Doo.
In the spring of 1979, ABC commissioned Scooby's 1st (and only) primetime special, Scooby Goes Hollywood, which allowed Hanna-Barbera the opportunity to parody some of ABC's primetime shows, including Charlie's Angels, Happy Days, & Donny & Marie, the latter of which was, I believe, ending its run around that time.
The plot calls for a little suspension of disbelief for hardcore Scooby fans. What looks like a normal episode of Scooby-Doo really has the gang on the set of their show, a la Famous Adventures of Mr. Magoo, if you will. Tired of retakes of hazardous stunts, Shaggy (Casey Kasem) and Scooby (Don Messick) decide the time is right to make a go at "the big time"---primetime, that is, and convince a network executive (Rip Taylor, The $1.98 Beauty Show) to let them screen a series of pilots that are actually the parodies I referenced. Each one is worse than the last. Take for example this excerpt, a pilot for Scooby Days.
Ironically, H-B would obtain a license for animated spin-offs of both Happy Days and Laverne & Shirley over the next two years. One interesting sequence has Fred (Frank Welker), Velma (Pat Stevens), & Daphne (Heather North Kenney, Days of Our Lives) recalling their first meeting with Scooby, a flashback that would be retconned out 9 years later with the introduction of A Pup Named Scooby-Doo. The trio then break into song, particularly a rewrite of the theme to the 1972-4 New Scooby-Doo Movies. Well, compared to Shaggy & Scooby's attempt at singing at the start, it's better than nothing.
This really wasn't my idea of a 10th anniversary salute to Scooby. A few months earlier, H-B & ABC served up another anniversary present in the form of, of course, Scrappy-Doo.
Where writers Duane Poole & Dick Robbins, two writers more closely associated with the Kroffts, failed was not allowing Shaggy to wear anything but his standard wardrobe. Would it have hurt for the ol' Shagster to break out a suit & tie?
Then again, H-B & ABC also whiffed on what would've been a real ratings blockbuster, pairing the Mystery Inc. team with the Super Friends, who could've stood the primetime exposure themselves. I would've taken that over this farce.