Then their control isn't the control but is the experiment group. If you're exercising under the species baseline norm then you're studying how sedateness decreases youthfulness, not how exercise prolongs it.

Humans were hunter gatherers, their level of exercise would be our evolutionary norm, IE the obvious control group. Exercise above or below our evolutionary norm would give us information as to how best increase longevity.

It's a commonly accepted 'fact' that our exercise below this evolutionary norm is detrimental to our health. Exercise above and beyond our social norm is obviously going to beneficial to our health and weight as it is equivalent to moving us towards our hunter gatherer ancestors, but this is only normalizing a wrong we already know about.