Why does merc use a 140 deg thermostat on carb motors and 160 on efi motors.

Is there some reason a 140 thermostat is better with the carb motors?

One possible explanation could be to reduce cylinder temperature to avoid detonation on a carbureted motor,
where EFI motors can use other means such as dynamically adjusting mixture and retarding timing.

My understanding is that the fuel octane requirement
decreases with the decrease in temperature