Comment by 827a

Its mentality. When told "Tennis is likely to have amazing health benefits", you could respond by saying "Sick, I'll integrate more tennis or sports like it into my life". In fact, one might not respond at all, and just do it. But instead, some people have this bug in their programming where they feel compelled to respond with a variant of "well, ahktually, tennis is popular among rich people so there's confounding factors at play which means you can't actually claim...."

The source of this bug is the same reason why when someone says "I wake up at 4:30am to go on a run", you'll 100% always get someone to respond "adequate sleep also matters, what time are you going to bed, you're missing out on important life events that happen after 8pm" etc. The cardinal sin is jealousy; getting up at 4:30am is hard, playing tennis multiple times a week is hard, the opposing side feels jealousy because they aren't doing something that's hard, so they need to find any way to minimize that hard thing they're doing to feel like equals.

Even you're doing this, and you don't realize it: "What's wrong with running at a normal time?". Nothing at all. Literally, seriously, no one even remotely implied there was anything wrong with running at a normal time. Someone choosing to run at 4:30am does not mean not running at 4:30am is bad; but you think it is. Why? Because it is true that running at 4:30am is harder. Harder doesn't always even mean better, especially when it comes to getting up at 4:30am, but it does definitely mean Harder. So: You minimized their strain by asserting that running at 4:30am is "not normal".

This isn't a university, and you're not a test subject. You're a human, who needs to take care of their body. Arguing about the minutia of the results of some research paper is Mindset; its forest for the trees. Literally, no one who adequately exercises would care that much about studies on tennis which adequately control for confounding factors, because they're too busy actually playing tennis, and they've seen and felt the positive effect it has had on their body and don't need a research paper to tell them its healthy.

(I'm just using tennis as an example here; there's plenty of other sports that follow this vein)