Are we sure that is "blindingly obvious"? I think the whole point of studies like this to try to tease out hints at what parts of it are genetic vs circumstance vs choices.

FWIW I think that the genetic component of 'innately happy' is quite small, as I've known relatively few dirt poor people who were happy anyway, and relatively more carefree upper class folks. Though of course it's possible it's still genetic and just caused economic sorting higher up the tree, I suppose.