It’s also not necessarily a net-gain. There are a bunch of trade-offs to being better able to deal with a lack of food. Specifically, by sacrificing body mass and brain development to conserve energy.

Surviving adverse conditions can mean developing novel evolutionary strategies. But it can also just amount to evolutionary downsizing. Living as a smaller, weaker, stunted version of your predecessors because the runt of the litter needs fewer calories to get by.