so why people keep making fun of it and not just be honest that they still end up being the next COD game every year?
It took 4 paragraphs and an inexplicable line break to get past your preamble and find out what your post is about - especially because the title is not descriptive.
In any case, there is truth in what you say. Gamers, game developers, and game reviewers criticize perennial games like Assassin's Creed and Call of Duty for not innovating, but these games still sell well. However, that doesn't make the criticisms inaccurate.
Did you know that on television shows like Two and a Half Men, How I Met Your Mother, and The Big Bang Theory get good ratings? One of the best-selling series of books of all time is the Twilight series by Stephanie Myer, and both Dave Matthews and Hootie and the Blowfish sell millions of albums. Do you get where I'm going with this? A game selling well does not necessarily mean that it is well-made.
Having said that, you are on r/truegaming, and this subreddit is usually read by and commented on by gamers who want to become game designers or game developers, so the criticism isn't the silly black-and-white that you see on other gaming forums. Most of the time, when CoD is mentioned, I read people talking about the merits of the series as well as the lack of innovation.
CoD is extremely AAA, and while I am burned out on the multiplayer, I still enjoy the single player for each new iteration. I'm a game developer, so I can easily just borrow someone's copy to play it rather than buy my own copy for the 6-10 hours of single-player, so I don't really "buy it anyway" like your post contends, but I do appreciate the single player and the fact that many gamers, especially those who only have consoles and maybe haven't had access to as many different multiplayer shooters as people who have been playing on PC for a long time, love the multiplayer. When the multiplayer progression and kill-streaks were first innovated, I really enjoyed it too. Now, I'm bored with it, but I still like watching people play it in the break room. They have good production values and higher-end kill-streaks are a delight to see.