For a vast amount of human history food has been much harder to obtain and less calorie-dense than it is today, so evolution has optimized for energy efficiency rather than raw power.
Significantly, and a large part of the reason why is energy efficiency. Humans have large brains that take a lot of calories to sustain, and because of their large brains didn't have nearly as strong evolutionary pressure to maintain musculature.
Probably the wrong way to look at it. They can exert greater force for shorter periods but the great apes have far worse endurance than humans. A chimp is about a third stronger than a human of equivalent weight but we can run marathons and they can’t. We have a higher proportion of slow twitch muscle fibres compared to fast twitch than the great apes.
