I'm of the view that injuries are random

I've gone through a week of matches and picked up 4/5 injuries, but also gone through a week of matches with no injuries.

I rarely use Red Packs to resolve injuries (although I have over 60 since the iOS update :-)) and tend to let them time expire

As has been said by many, there are lots on conspiracy theory's, but my guess is a randomiser is used in the game engine so it becomes 'the luck of the draw' fwiw