I didn't even put any thought into that, I just remembed a theory I saw so many times I just assumed everyone knew, but you, so I just mentioned it without even doing any research. Here is some:
There is a theory saying that since the first Scooby-Doo cartoon started in the late 60's, it was set during the Vietnam war. Because the army was drafting teens at the time, the gang was forced to runaway from home and relocate to Canada to avoid being drafted and going to war, which explains why in every episode they're always driving in their van with no clear destination.
Shaggy is your typical hippie with a case of the munchies. Being against war, he decided to take his dog, Scooby, on a road trip in protest.
Fred Jones is a military school drop out whose draft number was up, making him AWOL.
Daphne is (obviously) Fred's high school crush who can't bear the thought of Fred leaving and possibly getting killed in the war, so she joins the gang to be with Fred.
Velma is an anti-war activist who decides to join the gang on the road trip. > https://fantheories.fandom.com/wiki/Scooby-Doo