Because it's COD!
COD gets a bad reputation in the gaming community because many people say things akin to "Oh, I'm an elite gamer, I play COD and WOW". To other gamers, it just comes off as immature. Plus, I'm not sure if many people actually think the games are good. However, that's just their personal opinion.
To the OP: Haven't played COD, nor do I want to because gritty FPSs aren't my cup of tea.
The thing that annoys me about a large amount of COD players is their obsession with "realism" despite the fact that a Barrett M82 .50 caliber rifle weighs in at 40-odd pounds, and yet in MW2 you can RUN with it. Don't get me started on the impossibly fast reloads and the fact that you can apparently shoot down a helicopter with a .308 caliber light machine gun. Nothing against the game itself (not my style, but that's just opinion there), but a lot of the gamers I've encountered are incredibly annoying.
i'm pretty sure in real life soldiers learn how to run with the M82, but i don't know
ikr??!!! reloading is waaaaayyyy to fast! especially in World At War, they reload the bolt in a bolt action rifle waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay to fast! and when you reload a gun that requires putting the rounds in maunually, they do it too fast to! in Battleground Europe, the French have a rifle that needs to be reloaded one round at a time and it holds 8 rounds, it takes a long time, but its more realistic