I initially thought COD was in a position more like Madden or FIFA, but this kind of proves that sports fans are actually retarded if they continue trucking along with no changes yet people start ignoring COD
The thing about sports games is that the sports themselves don't actually change all that much over the span of a decade apart from team rosters, coaches, names and cities. The mechanics of the sports themselves don't change much at all barring the occasional rule change, which still generally takes years of pressure and deliberation by whatever league/club/body is in charge of it before it finally applies a change.
That's not to say it's "repetitive and boring," because obviously sports and sports games are massively fucking popular, just that you really
can get away with shipping practically the same game to fans every single year just with the updated number and rosters and it's okay because that's a pretty damn close match to the real sport itself. Maybe there's an engine tweak or control scheme update to make the game play better or something, or the graphics improve or get refreshed or whatever, but niggling details aside football from 40 years ago is still basically the same as the football that's played today.
COD and Battlefield cast a much wider net and can do a
lot more to be "different" with each release -- there's lots of IRL settings (Civil War, Spanish War, War of 1812, WW1, WW2, Vietnam, Korea, Iraq/Afghanistan, etc.) and with hundreds of real countries in the world there's countless fictional settings to dream up to set a war in, tons of equipment and timeframe options, real and fictional stories to spin, real and fictional characters to draw from, etc. Then there's other planets and shit too if they really want to go nuts. The stories themselves don't even have to make a lot of sense or be more than "just barely" connected -- how long have modern soap operas been running, to immense popularity?
Sports fans keep on trucking because they enjoy the game and the game doesn't really change much. COD and BF going "stale" is a baffling failure of creativity and talent. "Run around and shoot stuff" is time-tested classic game stuff. If you can't keep cranking out different "generic but fun war story game [current year]" you've got a braindead staff of creatively bankrupt morons.
Remember that South Park (ugh) gag of how Family Guy generates its scripts? Some fuckin' whales or something pick idea balls out of a pool and they just madlib them together into a script? That's literally all they have to do for COD. Pick a setting, a tech level, a plot theme, a Big Bad, and a Good Guy™. Then pick plot beats and elements out of a fucking bingo ball hopper, stitch it together, get it voice acted, put some Le Epic Orchestra™ music to it, and assuming you haven't fucked up anything technical (crashes, visual glitches, a gun so bad it angers the realism spergs, etc.), you've got a fun game. Mostly because the set dressing isn't critically important anyway -- it's not Halo or Mass Effect, it's "just" COD. You're running around and shooting stuff.
It's a soap opera with guns, how the fuck are they having trouble spinning out new ones?