Well I don't think adding a few more hrs of gameplay would make most FPS repetitive or boring. Too many times have I heard "Good game but far too short". Gears of War for example. I was just getting into it when it ended
Nope that's not a good enough reason. Maybe an average game would get repetitive and boring if extended but a lot of the qiality games wouldn't.
I don't play MP FPS games as the reason I play games is for a good storyline mainly and playing against other players offers no storyline at all unless you play Co-op I suppose. Playing against another player just to see who is best offers little interest for me.