Although Hanna-Barbera's decline was one reason why Scooby content went into a lull after 1991, another lesser-discussed reason is a cultural shift with Saturday morning cartoons. networks phasing out cartoons on Saturday mornings due to governmental legislation. In 1990, the United States Congress passed the Children's Television Act, which required networks to broadcast at least three hours per week of educational content. This caused networks to begin shifting gears with how they approached Saturday mornings. In 1992, NBC got rid of Saturday morning cartoons and aired only live-action shows with "after school special" types of lessons, such as Saved by the Bell. Other networks didn't follow suit right away, but all switched their formats within the next decade. CBS changed to educational programming on Saturday mornings in 1997, and ABC extended the hours of their morning news show and got rid of cartoons in the early 2000s (airing the required three hours of educational programming at another time).
In a sense, this shift was natural with the creation of television networks targeted towards kids, such as Cartoon Network, Disney Channel and Nickelodeon. Saturday morning cartoons were originally created because there were no networks airing only children's content, but as channels specifically for cartoons were created, there was less need to have designated time for cartoons on otherwise adult-oriented networks.
Of course, Hanna-Barbera's decline was the main reason for the lack of Scooby content following 1991, but arguably, the cultural shift is another small part of the reason that no new Scooby-Doo shows aired for a while after A Pup Named Scooby-Doo concluded. You can read more information on the larger cultural shift behind getting rid of Saturday morning cartoons in this article.
John Stephenson was famous for voicing a number of miscellaneous Hanna-Barbera characters, including 70+ characters and monsters in a number of classic Scooby-Doo episodes from 1969-1985 (and even voiced a few in What's New, Scooby-Doo?) John's last ever role before his death was voicing the sheriff in Scooby-Doo Abracadabra Doo, which is particularly special considering he voiced a number of sheriffs in early episodes of Scooby-Doo.
In "The Headless Horseman of Halloween" from The Scooby-Doo Show, there is an ironic animation error given the villain switches people's heads. In one shot, Scooby-Doo and Scooby-Dum's heads are switched on the wrong bodies! Thanks to ScoobyDooUK for coming up with this week's fun fact!
The artist who sings the chase song "Hong Kong Holiday" in What's New, Scooby-Doo's "Block Long Hong-Kong Terror," E.G. Daily, is also known as a voice actor for a few surprisingly famous cartoon characters. E.G. voiced one of the Powerpuff Girls, Buttercup, and is also the voice of Tommy Pickles on Rugrats.
"Scooby in Wonderland" and "Scooby's Swiss Miss" from The Richie Rich / Scooby-Doo Hour featured character designs by Jack Kirby, who was the man that created several popular Marvel Comics superheroes, including Captain America, The Hulk, and the X-Men.
Decades later, a character from What's New Scooby-Doo? would be named as a reference to another character created by Jack Kirby in 1978. Dr. Armand Zola from "Uncle Scooby and Antarctica" was named to reference Arnim Zola, a Marvel villain created by Kirby, who transferred his mind into a robot body to preserve his consciousness. Arnim Zola has appeared in both the 2011 Captain America film and the sequel.
The mirror doppelgänger scene that is seen in a number of Scooby-Doo episodes, including "Never Ape an Ape Man," "Mystery in Persia" and "A Scooby-Doo Valentine," is actually a trope that was made famous by a 1933 spy thriller. The film is a Marx Brothers' spy film, titled Duck Soup, which centers around spies trying to overthrow a newly appointed president of a country. You can watch the mirror scene that inspired the trope above.
Professor Pomfrit from "Big Appetite in Little Tokyo" (What's New, Scooby-Doo?) is a reference to Leander Pomfritt, teacher on one of the shows that inspired the Scooby-Doo franchise's creation, The Many Loves of Dobie Gillis. William Schallert, who had voiced Leander Pomfritt on Dobie Gillis, voiced Professor Pomfrit on this episode to further play into the reference.
Shaggy's name was not first revealed to be Norville until the post-Scrappy era of the franchise. "The Sludge Monster from the Earth's Core" from A Pup Named Scooby-Doo is the first episode where the name is ever used.
In "Now Museum, Now You Don't" from A Pup Named Scooby-Doo, the gang's teacher Ms. Takai tells the class that "konnichiwa" means "good morning" in Japanese. This is actually incorrect. "Konnichiwa" means "good afternoon," whereas the correct Japanese word for "good morning" is "ohayo.