If you consider when the franchise began, breaking it down by decade goes:
1969-1978 - First decade ends with The Scooby-Doo Show and Laff-A-Lympics; Scooby relative introduced and has become a more generalized mascot character.
1979-1988 - Starts off with meta commentary in Scooby-Doo Goes Hollywood and massive overhaul of series with introduction of Scrappy-Doo and sidelining Velma and Fred starting with 1980's Scooby-Doo and Scrappy-Doo. Series shifts completely over to real monsters.
1989-1998 - Kicks off with meta once again but with the entire cast and people in suits. Mostly status quo and mascot status for Scooby until ending with a return to real monsters in Zombie Island.
1999-2009 - Starts off with DTV films heavily focused on real monsters but What's New basically reverts the entire series to the 1970s and most films for the next decade afterwards are basically extended length WNSD episodes. Television show goes completely off the rails towards the end with Shaggy and Scooby-Doo Get a Clue.
2009-2018- Franchise goes in a really weird direction with Mystery Incorporated being a lore heavy deconstruction of the franchise, Be Cool basically metahumor self-parody, and the DTV films being often bizarre crossovers.
2019 - Kicks off by reverting to the Scooby-Doo Movies format.
Looked at it that way, it's pretty much a ten year cycle of In/Rein-venting Series, Series Shifts Back to Status Quo.