The brains we did end up with are really bad at creating that sort of knowledge. Almost none of us can. But we’re good at communicating, coming up with simplified models of things, and seeing how ideas interact.
We’re not universe-understanders, we’re behavior modelers and concept explainers.
My guess is that it's not dumb luck, and that what we evolved is in fact general intelligence, and that this was an "easier" way to adapt to environmental pressure than to evolve a grab bag of specific (non-general) cognitive abilities. An implication of this claim would be that we are universe-understanders (or at least that we are biologically capable of that, given the right resources and culture).
In other words, it's roughly the same answer for the question "why do washing machines have Turing complete microcontrollers in them when they only need to do a very small number of computing tasks?" At scale, once you know how to implement general (i.e. Turing-complete and programmable) computers it tends to be simpler to use them than to create purpose-built computer hardware.
Because deep abstract thoughts about the nature of the universe and elaborate deep thinking were maybe not as useful while we were chasing lions and buffaloes with a spear?
We just had to be smarter then them. Which included finding out that tools were great. Learning about the habits of the prey and optmize hunting success. Those who were smarter in that capacity had a greater chance of reproducing. Those who just exceeded in thinking likely did not lived that long.