Probably because judging footballers on goals and assists alone is daft. Obviously the stats for all of them are still outstanding, but I'd still have KDB ahead of Salah.
Sorry, but that's mental. Salah is going to break the all time PL goal record in his first season. To even be close to Messi/Ronaldo stats is absolutely amazing.
Saying that, I enjoy watching De Bruyne more than Salah, but there's no question who deserves the award for player of the season for me.