Lead programmer doesn't want to implement or try new things because the production guys decided we have 4 months to make a game (or hell, just cause he wants to be lazy or doesn't want the pure stress of bug finding and fixing). Or maybe the lead designer doesn't want anything complex or interesting because it's harder to implement so the level design or mechanic design falters. Sometimes the big boss comes in and says "we want it to be like this!" then they walk away to leave others to figure out the mess (which ultimately doesn't work but who wants to get fired for not doing it?) Sometimes they just overwork the staff so much that there's not a lot of enthusiasm or motivation to make anything new or interesting because who has the time/energy for that when you're already working 14 hour days for weeks? Sometimes they switch staff around so people who started the game aren't the ones who finished it. And some people just work in the industry because it's a job, not because they absolutely love making games, so they're not trying to do anything but finish their workload and go home to their families.