Call of Duty: World War II is having a big of a problem at the moment with players not actually competing in matches. It's specifically a problem in the Gun Game mode. The reason for this is a Special Order currently running that requires players to complete 80 multiplayer matches. The prize for finishing this order is the ever coveted Epic Bribe and Resistance Uniform Bribe. If you get an Epic Bribe, you're guaranteed an Epic item, which you can't get in standard loot boxes.
Players would obviously very much like to complete this Special Order, and 80 matches are nothing to sneeze at. Playing regularly, assuming matches take about 10 minutes to complete, you're looking at 14 hours of game time in order to get that Epic Bribe. Seeing as how most people either don't have that kind of spare time, or don't want to devote it to Call of Duty: WWII, they're finding other ways to win.
The easiest thing to do for achievements that require players to complete X number of online matches is to AFK. Even further, in Call of Duty: WWII, the “best” game mode to AFK in is Gun Game. Gun Game gives players a random gun and when they use it to get a kill, they are rewarded with another random weapon. This continues through 18 tiers and whoever gets a kill in that top tier first wins. If no one reaches that top tier in time, then the person who made it through the most wins.
Essentially it's the one game mode that completes the fastest and doesn't affect your stats. This makes it prime territory for AFK-ers seeking the reward from the current Special Order.
Obviously, this is a really big problem for those who just want to play the game. Sledgehammer Games hasn't spoken out about the issue yet, but here's hoping they do soon.