So, water is wet.
I would also argue that it isn’t necessarily true in the strictest way of thinking, because personally if I had infinite money and technicians to maintain things I’d have 70s-90s sports cars before everything got massive and wide and heavy. That’s way more expensive and luxurious than a new Model 3 or something.
There has to be some incredible correlation between having the time and money to play tennis “a few times per week” and being significantly wealthier than the average person. And being wealthy is clearly the healthiest thing you can do.
So then it's a bidirectional correlation. You're more likely to be fit if you are wealthy and more likely to be wealthy if you are fit.
Essentially, what you're looking at is that people who engage in self improvement end up better off than those who don't.
It's a priori obvious but some people are uncomfortable with it for some reason - trauma response / coping mechanism, something like that.