Jackson LeRoy Briggs
You think you bad? You ain't bad!
The original Scooby Doo series is set after a horrible economic depression. Everything is abandoned and falling apart, and all of the villains are people who would normally be really respected (professors, museum curators, celebrities) who have fallen into hard times just like everyone else.
And that also explains why a bunch of teenagers can do what they want unsupervised. shyt is literally every man for himself.