There is difference between multimillion franchise like CoD and niche games like DMC. CoD devs wont even notice if somebody hates any changes they make to the franchise, because couple of fans left, thousands of kids will still be there. Niche is different story. As much as somebody wants to believe otherwise niche games exists thanks to loyalty of the fan bases. Complete change in direction will lead to fan base split, and since niche games can't boast 30 mil sales it jeopardises whole franchise. We all know what happens to niche games without much fan-support, like we saw with Lords of Shadows, PoP reboot and Darksiders.
Unless a franchise does something to step out of that niche zone it will never expand its fanbase. It's fine to get a group of loyal fans who like your product but at some point those fans will likely move on if something else comes along. Hard to keep old fans happy while introducing more mainstream ideas to bring in wider range of fans. You may split a fanbase but if you can please both fans with games then you could essentially get best of both worlds.
With the amount of hate & internet memes directed at CoD I'm sure the developers are well aware of people views on the series. Hence why it's jumped from WWII, to Modern Day to Futuristic and all over the place. They are too busy trying to cater to ALL fans and ALL opinions that they forgot what made CoD become that multimillion franchise in the first place.
As a developer if you simply accepted every suggestion the fans made and didn't include your own knowledge and ideas I can guarantee the game would be awful. Would be so cluttered and like a 100 people giving you directions to a place from where they live, you wouldn't know what direction to go in to begin with.
Series has changed so much since the originals that were actually quite niche games being PC exclusive WWII titles (which at time weren't big yet). The sales have dipped and gamers opinions are changing but people still buy it who say they hate it so why would they stop doing the same thing over and over?
Compare CoD (original on PC) to latest and though formula is similar the game feels like something totally different. As much as people say that it's recycled every year (which it has been lately) it's changed A LOT from what it once was & in many people's eyes not for the better.
The TV adverts cater for the exact stereotype of CoD fans and there is a reason for that, those are the people who mindlessly purchase it every year. Same people who say how bad it is then rinse and repeat same thing the next year. Same thing that's starting to happen with Assassins Creed series already & heard nothing but abuse for Destiny lately yet read today that it's now hit 25 million players so more and more people are still playing it.
Developers are human and they do have feelings and lots will be unhappy with MANY aspects of their games when they release. Many will actively try and rectify these issues and see how they could make them better and criticism hurts a lot of them too, regardless of sales.