Sony has released the player counts for almost every PlayStation 4 game over the last few days. It’s unclear if this was intentional or not.
The My PS4 Life service that was launched gives you a specific stat about how many people earned a specific trophy for each game. People are now using that stat against the percentage of people who have earned each trophy to work out how many people have played each game on PS4.
Obviously, this site was created some time at the end of November, so recent games like Fallout 76 or Red Dead Redemption 2 have probably seen an increase since this went live.