Protagonist Iden Versio is in the centre of the box art for Battlefront 2. Time spent doesn't necessarily equal value in games, but if something feels short, you can't help noticing it as a player. If I was a Star Wars fan, buying this game mainly for the promise of EA's first big budget story with the licence (TOR aside)-and those people are bound to exist, given the wide audience that loves these movies-I'd be a little disappointed.
Star Wars Battlefront 2's campaign took me around five or six hours to finish, and the people on How Long To Beat say they've done it in 4.5. If singleplayer is still a big part of why you enjoy playing FPS games, then it's hard to justify spending £50/$60 for six hours. The campaigns in shooters like the original Homefront, Battlefield 1 and Titanfall 2 range from 4.5 to six hours in length. For the most part, other developers followed its lead. Modern Warfare 2 took 6.5, and the series has lingered there ever since. According to one of my favourite utility sites, How Long To Beat, COD 2 took an average of 8.5 hours to beat.
When did five or six hours become the target length for a shooter campaign? I think it was during the journey from Call of Duty 2 to Modern Warfare and then Modern Warfare 2.