For me, and I suspect a few others, playing the major sports competitively as a young person and into adulthood has done some damage to knees and ankles. Old injuries and the pounding of other stuff like basketball and running increase the degenerative effects of getting older, so cycling is the major part of my low-impact workout and because I can work as hard as I can/want to in a short amount of time and still have time free for work and home projects - as well as the fact that I flat-out enjoy it.

Also, are you saying that your overuse injuries went away after you started eating meat again?! Are you stating this as coincidental, or do you attribute this to something specific (if something specific, gotta' use that one on my wife, who is a non-red meat eater).