I think one of the mistakes most of us probably make about living like a cave man is to assume our unconscious cultural norms apply.
Years ago I read an article about the challenges and pitfalls of globalization. One of the anecdotes reported was that car manufacturers who opened factories in Mexico and tried to approach labor from a US/European perspective had tremendous difficulty keeping workers on the job. Not a problem finding people who could do the jobs, but getting them to come in to work every day. You know, like 99% of workers in the 1st world do. Workers in these car plants in Mexico would work a day or two then stop showing up until they needed more money.
In the US it can reasonably be assumed that you (or any worker) will keep working as long as someone is willing to pay you more. It isn't hard to find people willing to work 70+ hours a week. That's arguably changing (the whole "life balance"thing) but that's mostly for salary jobs than hourly. The fact that I could survive on $10k/yr, or pretty comfortably live on $50k/yr, hasn't caused me to throttle back and work fewer hours once I passed those milestones. A 20% raise wouldn't cause me to cut my hours by 20%.
But that's cultural. It isn't how everyone behaves, as the people opening car plants in Mexico discovered. The solution to their problem was pay cuts, until the workers needed to work 40hrs/WK to survive. Without doing that, the workers just didn't see the point in showing up. The difference isn't genetic, isn't a matter of intelligence, it's cultural.
So... We assume that if Grok had unlimited fruit, or meat, or whatever, Grok would fatten up. Another perfectly reasonable hypothesis is that Grok would spend less time on survival and more time having fun, which of course naturally tends to produce a lot of Groklings, and soon the abundance wouldn't be sufficient. It just depends on Grok's cultural framework.