Activision patented a new SBMM system in April 2019 (6 months before the release of Modern Warfare). The new SBMM system doesn't just take your K/C, SPM and W/L anymore... It calculates everything including your movement around the map, the weapons you use, purchases and more.

The patent states that a part of the system is designed for "influencing game-related purchases", which means players that have COD points or a tendency to buy COD points could be matched with players that have purchased in-game items to entice them.

From what I've read, the patent also has zero mention of prioritising connection based matchmaking over skillbased matchmaking - Which Activision calls the "Virtual Coaching System". So a casual playing experience and a good connection is second to $$$ (kind of expected lol).

Although there's no evidence to support that the system was implemented... It does explain why Modern Warfare's SBMM feels so much stricter and stronger to the previous Call of Duty titles. It makes sense that they needed to recoup lost revenue from the removal of supply drops.