You’ve never played CoD then, or CS.
Ever play World at War? That was one of the more egregious examples of combo wins, but it kept up through Modern Warfare, Modern Warfare 2, Black Ops, etc. You get three kills, you get a bonus, which gives you more kills, which gives you more kills, which gives you more kills, which wins the game. Turrets and gunships did get patched so they no longer count towards kill streak bonuses, but you should still shut them down. It’s a good habit to get into for most games and can have a large effect on the game. In Battlefield, taking out the top player deprives the other team of a disproportionate amount of skill, same in Combat Arms, Brink, etc. The only time it doesn’t matter is in non-team games with instant respawn, then it’s checking kills. Which as they are the only measure of skill in such games makes sense.
And you know it. 
EDIT: I say this not as someone making excuses for CoD players (appalling game outside of the ninja builds), but as an old Quake player who spams scoreboards in most games. In LoL I want to know who’s getting ahead, in CoD I want to shutdown killstreaks, in CS I want to stop people getting AWPs and dakdaks, in Battlefield/Brink I want to stop the influential people from bringing their team up, etc. I do play more of an assassin than a spammer, but that’s my reasoning which came before the action. Again not all people do that but it’s generally either a valid measurement of skill, or a valid strategy, not just “killwhoring”.