Time is money and money is time, and nowhere is that more obvious across all entertainment than with video games.
Where you'll see everything a movie has to offer in around three hours or less - or you can get through the majority of books in an afternoon or day of concentrated reading - scores of triple-A titles can stretch into the hundreds of hours, just to see a narrative conclusion.
The question of "But why?" very rarely comes up, but it's likely down to a furtive industry escaping the arcades and testing the waters with interactive play-spaces, and the reality of keeping a premium unit cost per game.
Discard the notion of a game "needing" to take 50+ hours though, and there are scores of recommendable titles you can clock in afternoon. Or even better, in under an hour.
Rare is the mix of ultra short design and actual quality, but that only means the cream of the crop is that more recommendable.