Injuries just happen - got a 35T team that, iirc is now at 13 injuries for the season (not staggering but significant); the other 35T has had 3 and my main has had 3 or similar. I suspect that like everything else the relevant RGN has a quite wide range and when it goes against you it wipes out all the positive factors like morale, pitch etc quite easily. Improving facilities etc will help (and imo you should do it) but it can't protect you. Sometimes it just happens and you notice more when it happens in clusters.

PS I recall a period at Glasgow Rangers where it seemed like a high proportion of new signings suffered injuries quickly. It happened often enough and persisted long enough to seem like more than luck, a pattern was seen, and then it went away.