OP is a little too cavalier with his conclusions for my taste. Jerry Rice got a LOT of breathers, working those short routes over the middle. (Even under the old rules, when guys could go head hunting, there was relatively little risk of Rice getting the typical physical abuse, what with the insane accuracy of the two guys who were throwing to him.) Johnson runs a LOT of deep routes. Plus he blocks aggressively. This HAS to have an effect on him. How much, I don’t know, but I’ve a very clear picture in my mind of Randy Moss, loafing about like a man without a care in the world, when his name wasn’t called. It’s a damn sight harder to show up for every play.

It is a combination of age, injuries, and motivation. In Holt’s case, it was more about injuries. The aging just accelerated the process.