The problem with pac cabs is that the artwork is painted on, its not silkscreened like later games. They were obviously the most popular games, many of which are still in service today, so naturally they have been exposed to the elements much more than other games out there. We all know these are also notorious for "hand wear", which is a given considering theres no fire button in the game, you just move the joystick around with one hand.
Stencils are expensive and you need skills to properly use them. Repro art is also expensive and, while its probably easier to apply, just dosent look "original", so some collectors stray away from that as well. Not to mention most of what you see belongs to Joe Schmo who usually knows nothing more than "Hey, it's Pac-Man" and believes "wow, an actual arcade game, and it works too, these are worth alot of money".
Heres mine. She's not perfect, but not hideous either. Personally I opt for this look anyway. It's cheaper and it adds charm and character. Only cosmetics I've done is a new marquee and fresh paint on the coin door. Otherwise it's all original (with the exception of the backlit cherry red start buttons).