Why is every person involved in a movie listed in the credits?

Movies have huge credit rolls that tell you everyone involved from the director down to the person who made the cups of tea. But why? I can understand why actors, who need exposure to maintain a career, would want this. But is it important for the person who drove the truck full of props around to be credited for their future prospects?

You don't see a plaque when you walk into a building listing everyone who laid a brick as part of the construction. I assume there's a historical reason why the entertainment industry, and only the entertainment industry does this.

Edit: To all those that took my geniune question about what historically lead to this, and turned it into accusations of me being some sort of thoughtless "asshole", what is even the point of someone trying to contribute to these online communities if you are just going to be made to feel horrible?