It's not the exact same game released every year with slightly better-looking dirt
If we are attacking the amount of games a developer makes then I encourage you to go and look at the number of titles Bethesda has worked on since Oblivion, and the number of titles Treyarch/Infinity Ward have worked on since CoD4.
If it is the gameplay we are attacking then I encourage you to go play CoD4 then MW2
If it's the graphics we are attacking then you should understand the huge difference 60fps makes to a shooter versus 30 fps because CoD runs at a consist 60 fps on consoles which BF doesn't.
I could go on but honestly there isn't a huge difference between Oblivion vs Skyrim, nor is there a huge difference between CoD4 and MW3.