Because it is a wonderful cliche' that harkens back to the original Scooby Doo cartoons. The show usually began with the crew traveling somewhere in the Mystery Machine, and would stumble upon a mystery to solve. I guess they have replaced Scooby Snacks with zagnut bars! ZOIKS!
Think about it, the character parallels are obvious.
Fred- MM because he thinks he knows everything, and "is the leader."
Velma- Ranae, because she uses common sense, logic and critical thought to solve problems.
Cliff- a male character niche of Daphne- aware, dedicated and is a team player.
Shaggy- Bobo, because he looks kind of like a hippie and always encounters the monster.
Scooby Doo- Monkey, because he's a dog, and hangs out with Bobo just Like Shaggy and Scooby were inseperable.
The show even has the old plot of "hey gang, let's split up and look for clues!"