fuel issue after car sits.

i still find it hard to believe the fuel evaporates all the way down to the pump in just 1 day or even a few hours? i can see the fuel evaporating from the carb there is more surface area in the bowl but 5/16 line only has a tiny little bit of srface area, on my car the filter will be bone dry. i think everyones cars would be averaging 10-12 mpg if this was the case.