It is no surprise that Skill-Based Matchmaking (SBMM) has been one of the most controversial topics in the Call of Duty (COD) community. To describe it in simple words, SBMM matches players with the same skill level against each other, in line with the game's competitive nature being based on individual players' stats.
SBMM is essentially found in competitive playlists and ranked matchmaking instead of casual play. The majority of COD players are against SBMM, including renowned professional players such as Nadeshot. Nadeshot also recently talked about SBMM in a follow-up tweet to his earlier SBMM rant.
Nadeshot believes that SBMM is good for both beginners and experienced players, but the way it has been presented in the game is incorrect. The reason why having SBMM is good is because it keeps lower level and beginner players in a "protected" bracket. Some players have lower skill levels, and they won't be able to play against players who are always "sweating" their way into the game.
SBMM was also found in Modern Warfare (2019). Activation, however, at first denied that it ever existed in the game, and players later proved that it existed with several test runs. Following that, Activision finally stated that they have "implemented" SBMM in the game. Meanwhile, players and the tests done by them showed it was already there.
Many players have requested that SBMM be removed and replaced with a separate ranked playlist, but to no avail so far. Yes, SBMM protects the lower-skilled players, but it also takes the fun out of the game for those who do well in just 2-3 games.

