I suspect a couple of other factors as well. Like humans it does not have to be one big trauma. It can be a serious of smaller traumas, until the ccl fininaly lets go.
Also dogs can be pretty stotic, they can not talk, and do no express when they are having some discomfort.
But they are also pack animals with millions of years of evolution. Were they to express pain they would have been cut out of the pack, and left to starve.
So I believe they tend to go on as long as they can, without expressing pain. until it gets to that point they can no longer go on.
In hindsight I believe my dog was giving me signals that the knee was sore. But being a dumb human I did not pick up on them. Something I regret.