Call of Duty players want PC Gamers out of crossplay and their reasoning is pretty sound. Crossplay gaming in Call of Duty has pleased its playerbase allowing them to play their beloved franchise's games with their friends across consoles and on PCs. The issue that has cropped up with crossplay is the influx of cheaters the game is seeing with the PC users.
PC users, apparently, have become the vast majority of cheaters in Infinity Ward's Call of Duty games and Warzone players in particular have been having their healthy competitive environment ruined by these kinds of players. Infinity Ward has done plenty to combat cheaters and have consistently said "We [Infinity Ward] have zero tolerance for cheaters".
One player, Doni Tongakilo, has even started a petition to ban PC players from crossplay making it only an Xbox and PS4 area. The first line of the petition is as follows:
PC Hackers have ruined our fun way too much, almost on every enjoyable game. We don't appreciate hacking, aimbotting, red boxes etc. We want to see an end to this, once and for all!- Doni Tongakilo
The petition has 12,860 signatures at the time of this article being written and it seems to be increasing consistently. Whether or not Infinity Ward will see this and act upon it is a different story. I would imagine it would be fairly dangerous to ban an entire group of players from crossplay as hackers make up a vast minority of players. After all, the hackers affect the non-hacking PC players as well.
Infinity Ward has been doing a lot to counter-act hacking and ban cheaters worldwide and hopefully they can continue to minimize the occurence of hacking in their games and keep crossplay inclusive to all players.