Adding to what Warhead mentioned about depth, I think a big part of the injury problem is how the team was built. For the first 15 or so years of the Snyder era, the team did not draft lineman in the early rounds. Finally, by fortifying the DL this past year with Payne and Settle, our DL was good, young, and deep. Linebackers didn't have to take on guards and tackles. Our leading tackler wasn't a safety. Voila! Our defense was actually pretty healthy last year. Yeah, there was still flukey stuff like Dunbar's nerve issue, but that's football.
Conversely, our OL wasn't addressed. LG was only filled by Lauvao late in free agency. There is a reason he was available cheap. The turning point of our season was the Atlanta game (NOT Houston) when Lauvao and Sherff went down. That's when the dominoes started falling.
Cooley addressed all of this in a podcast. I think the Skins will fix the interior OL this offseason and the injuries will drop off on that side of the ball as well.