People also rage about being panic knifed in a shooter known for being a twitch, e.g. drop shotting and jump shooting. Compare BO2 to MW2 for knifing. Also, people hate being killed by shotguns that have a range more than 1m, while using SMGs themselves.
It's probably only popular in the US. I don't notice much of it in UK lobbies. It's happens a little bit with weapon variety. If I see good representation of Accuracy International rifles I know I'm in a lobby predominantly from the UK.
Because its the most unrealistic and the most abused use of a weapon class in the game.
Most players hate it and I hate it go and write a book defending it for all I care.
Like I said as soon as their is a viable alternative without quick scoping I'm out of COD like a frog in a sock.