Well, they need to give credit to everyone.
The directors, producers, development teams, voice actors, game testers, localizaion teams for every single region the game is released in, the other companies that were involved in the game and then they need to throw in some kind of special thanks at the end.
Oh, and you can't forget about all the babies that were born during development! That's the most important part.
Most games now give you the option to skip the credits, but still some don't. And you never do actually skip the credits, because sometimes games will treat you to something if you watch the credits all the way through. Maybe a little video or some kind of achievement or something.