For some reason, the temperature difference from the poles to the equator was much smaller at that time than it is now. Explaining why is an open challenge known as the equable climate problem.
> BAYSPAR measurements indicate extremely high sea surface temperatures of 40 °C (104 °F) to 45 °C (113 °F) at low latitudes,
I'm going to take a wild guess that humans aren't doing so good near the equator with 45°C oceans. Though it's definitely interesting that the temperature gradient flattened out so much.
