I thought these studies often control for additional factors like wealth, education etc. not sure about this one, but genuinely curious whether I am mistaken and science “did not figure it out” yet
It's 100% unsurprising that this is true of fitness too. This is what always happens. You look at something like a corporate health fitness plan and you find some correlate even after you 'control for' SES, prior health record etc etc; wonderful! Then you do a randomized experiment and it turns out that the residual confounding was still larger than any causal effect which might be there: https://gwern.net/doc/statistics/causality/2022-wallace.pdf Ah well. Maybe next time you'll manage to 'control for' the confounders...