It depends. When does the game run out of content?

Like if you make a game of say 3 hours but someone says "the game should have 10 hours of playtime" so you just add in 7 hours of worthless stuff then optimal time of the game is 3 hours.

A classic example of this is "open world rpgs". Yeah the story is 5 hours but if you climb all towers, which are 1 of 3 templates of which there are 200 towers , and defeat all the bases, which are 1 of 4 templates of which there are 300 bases and ride a horse across the equivalent of 500 Sq acres of small empty barren hills, the game takes 150 hours... Take the money for all that development time and make the story better.