Scoob is a little slow
This is the real answer. Away from the monster isn’t how Scooby think of safety. Close to his pal is!
Shaggy can also consume a Dagwood that’s twice the size of his own head in a single bite. He’s not human. He’s a cryptid.
Well he did run track as well as being a gymnast
In the 2002 live action Scooby-Doo, Shaggy breaks out into dance to try and maintain his disguise. He really gets into it and gives it his full power, which is unfortunate for the guy who tries to sneak up behind him to take Shaggy down. Shaggy never even acknowledges that he noticed the man, just the sheer power of his dance moves are enough to destroy the poor man by accident.
Jinkies.