I can't remember which season it was, it might have been 2016, but the Chargers suffered a weekly season ending injury which was usually ACL related (Keenan Allen week one, Jason Barrett week four are the two I can remember). Last season I think they had a few players suffer them as well. They seem to be unlucky injury wise.
But the thing to keep in mind is that players now are typically bigger and heavier than they were in past eras. The issue with being bigger and heavier is that it puts added strain on your body. Now you can obviously add more muscle to your frame and get bigger and stronger, which is fine to a degree, but what doesn't get bigger and stronger are your ligaments and tendons (etc). So I can add 20lbs of muscle to my 185lb frame, but even though I could add size to my arms and legs, my knee ligaments aren't going to change nor will my Achilles tendon (etc), and as such my body will have to cope with the extra weight. If you're lucky you stay healthy, but a lot of people that push their bodies to the extreme can suffer injuries when their body says enough is enough. It doesn't take a lot to tear a knee ligament when you're carrying a lot of added weight and being asked to do what these athletes do for a living.
