We don't need character development. We know Indy. We know Marion. We don't need to know the villains, because Indy villains are caricatures anyway. (This is not intended as an insult to the movies, since they are exactly what they're trying to be--boys' adventure novels onscreen.) We don't know "Mutt," but I think we get to know him well enough, ditto Ox. The genre provides us with just the level of character development it requires.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"