I prefer to think that whatever causes obesity, also causes knee cartilage degeneration. But then, if there is knee cartilage degeneration, excess weight will excerbate the problem, i.e. lifting heavy stuff (or one's own excess fat tissue) for example. Ironically, the best Olympic lifters are all pretty much overweight if not outright obese. It's ironic because that excess weight serves to lift heavier through some mass transfer (or some other term I can't quite think of) like a pendulum or counterweight, i.e. throw this mass this way to get that mass to go that way. This principle is also used for the disc and hammer throw.

An example: https://www.youtube.com/watch?v=zkGFAZK-7zM

It seems the implication is that the excess weight (over time) is the cause of knee cartilage denegeration (over time). There's scant data on that, but plenty on plain injuries like impacts for example. One text I found claims that Olympic lifting has a very safe record in terms of injury. If we believe that, then we have to wonder why we also believe obesity could cause knee cartilage degeneration. Consider that Olympic lifters practice endless hours with heavy weights. This extensive practice means likelihood of injury (from a lack of skill) goes as low as it can, hence the sport's safety record. With obesity, we live with this excess weight 24/7/365, evidently that's a whole lot of practice. So why the knee cartilage degeneration? It's not the weight, it's certainly not a lack of skill, must be something else.