You must have missed those threads then. Sports games are a constant source of frustration given that you're forced into getting a brand new game every year just to keep your roster current. It's mostly EA games that are blamed for this, but sports games have been ripped on for a while now.
The big difference though is that there isn't as much in a sport to change as there is a shooter. Sure you have to get the animations down for the new players, and you have to make sure you have all of the rosters right, but there isn't much you can change. The arenas are the same, the game is the same, the camera angles remain the same because they're usually based on watching it on TV, etc. It's refreshing to see a new mode or a tweak to the controls but in general they don't NEED to change as much.
Shooters are different. The only constant is that you're in 1st person view and you have a gun. Everything else can be changed... the environment, the type of guns, whether or not you get to use vehicles and what vehicles you use, etc. So when things feel stale in the shooter world, it's because the devs didn't branch out. There's no rules to stop them... Call of Duty was a WW2 shooter until CoD4 when they decided to branch out, and it's been absolutely dominant ever since. CoD4 showed that you can radically change the environment, weapons, time period, and multiplayer setup to give a boost to the series. There hasn't been anything like that since so it feels stale.
Sports don't have that freedom, so they're excused a bit for recycling. The last huge change I remember in a sports game was when NHL09 broke the mold and used your right analog stick for deking and shooting. The result was so intuitive and different it changed how hockey was played on the consoles. Nothings really changed since then though.