Question: If the airport and a plane don't allow dogs, then why is a cat is allowed on a plane?
Answer: Probably because the cat is smaller and well-behaved. If Scooby wasn't on the plane, that cat would probably stay in its owner's lap the entire flight and not get into any trouble.
Answer: Well before boarding Shaggy said they wouldn't allow large dogs on board. Implying smaller dogs would be OK.
Answer: Maybe because cats are smaller than dogs and all felines are relatively the same size and fit into a small pet carrier. Dogs range in size from a few pounds to over a hundred, making crating them more difficult.
raywest ★
I should add that this being a movie, they make up their own rules about things to serve the plot. It's unlikely in real-life that an airline would ban dogs entirely, though there may be size limits.
raywest ★