A friend of mine is a physio for an NRL team. I remember him telling me that there would be at least 1 knee and 1 shoulder reco per annum on average in both first and reserve grade so 4 season enders. That doesn’t include all the other injuries. Some times teams are just blessed/cursed (in our case) with outlier seasons.
I agree for the most part injuries are just back luck and misfortune.