Actually, Scooby's streak of TV shows has been much fewer and further between than what it was in the 70's and early 80's. So far since 2000 we only had 3 shows, What's new Scooby-Doo? Shaggy and Scooby-Doo get a Clue, and this one. in the 1960's-80's there were just so many... Scooby-Doo, Where Are You! The New Scooby-Doo Movies, The Scooby-Doo Show, Scooby-Doo and Scrappy-Doo, The All-New Scooby and Scrappy-Doo Show, and The 13 Ghosts of Scooby-Doo. Then after A Pup Named Scooby-Doo there was a very long hiatus until sometime in the 90's when they made the DTV movies. Then the live action film came out after all the interest brought back by said movies and non-stop Scooby reruns on CN.
There are a lot of characters that have the fortune of being always on in some form or another. Other than Scooby, the only characters that can hold that kind of attention are comic book super heroes. Spider-Man and Batman especially.