Some of its luck. But I've gone back and forth endlessly with my brother, a Packers fan, about this. He feels it's all luck, and that only bad luck is the reason the Packers have an excess of injuries seemingly every season recently.
I just don't buy it. I think that, for some teams- if you get hit by the injury bug every year- there is something wrong with the strength and conditioning. Just depends. I do think our 2015 injuries were a bit of bad luck.