Our bodies and responses were "designed" for such a system where obesity is impossible. The mechanisms that power obesity are vital for the survival of the human race.

The agriculture revolution only happened 10,000 years ago. This is all very new to us.

The real agriculture revolution only started in 1913 with the invention of the Haber-Bosch process for manufacturing fertilizer from fossil fuels. That's what really enabled excessive carbohydrate consumption for common people. Before that, humans were barely scraping by and it was still common for poor people to starve to death, even in relatively advanced countries.