Why do golfers get bad knees?

Twisting and loading: Golfing requires a fair amount of twisting movements. If you walk a hilly course, this can make your knees sore. However, the literature on injury patterns does not identify golf as a sport that has a higher than normal proportion of knee injuries although it can happen, especially in golfers with slightly abnormal knees to start.

Overuse injury: Most likely it is due to overuse, but it could be due to a lot of different reasons. Have it evaluated by a professional and get the appropriate treatment.