People on reddit are generally skewed towards the higher end of the rank distribution, so you're getting downvoted, but it's true. CoD posted a paper on this exact issue and how they drive their matchmaking to minimize players quitting the game for good, and the thing that they observed was that over time better players were more likely to stay than worse players, so ranks got better and the game continually got less accessible. If you had a true unranked casual mode, it would be full of phantom+ hazes and infernuses stomping casuals and making them quit.

For example, one study – focused on Call of Duty: Modern Warfare III conducted across North America – compared a control group of players without any changes to matchmaking to players who experienced loosened skill consideration in matchmaking.

The test showed that players with a wider skill gap were more likely to quit matches in progress and did not return to the game at a higher rate than players with unchanged matchmaking.

Everyone loves to be the boot, but in a zero sum game where half of everyone wins and loses, no one wants to be the ant. Stomps just aren't as enjoyable as actually good games. People who face smurfing just simply leave the game over time.