It's not in our nature, it's in the rewards we desire.
We desire the best mate possible. No industrial or computer advance has (yet) provided any of us with better mates. Mates are as scarce as they were hundreds and thousands of years ago.
Mates choose each other according to relative status. By definition, there is no way we can increase everyone's relative status.
So the reason people grind as hard as they used to is that they're facing the same incentives and barriers: For the mate you want, you have to grind your way up the status hierarchy (or at least enough to avoid falling). Competition is just as stiff as it was in 1950 or 1850, or 1000 BC.
Things will only truly change in this respect when we invent artificial ways to satisfy peoples' desire for mates. However, this won't happen soon. Sexbots are only a small part of it; a mate is much more.