It turns out Pgh wasn't going overboard with lifting heavy free weights in the season - they are doing the exact opposite, and THAT is likely leading to all the injuries. It turns out that Pgh mostly uses machines for weight training, and THAT is the problem. Machines don't allow for the huge benefit of muscles stabilizing the chain and core, which is a huge benefit of free weights. That would explain why SF was so low in injuries, because they do lots of free weight work.
Reality is, Pgh has only two power racks in their entire gym. Sources say they use more machines than any other team and free weights are virtually non-existent. My source says every single NFL team uses more free weight training than do the Steelers.
So, I was right in that something in their training was likely to be adding to injuries, but it was the exact opposite of what I thought. It appears Pgh is pretty lax in what they require players to do in the weight room, and they are under the false belief that cutting out most all of free weights is safer. They are not benefiting from the stabilizing effect of free weight training, as all other clubs are.