Why do hurricanes, the worst storms at sea, last a week or longer and measure hundreds of miles across whereas tornadoes, the worst storms on land, are measured in hundreds of yards and rarely last a single hour?
Hurricanes and tornadoes are different kinds of storms and it is an error to compare them in the way that you have. It’s true that hurricanes form over warm ocean water, but tornadoes occur over oceans as well as land (though far greater numbers of them form over land). Hurricanes are low pressure systems that derive their energy from warm ocean water. They form relatively slowly, often taking several days to achieve winds of hurricane strength (at least 74 mph). Tornadoes are not “independent” storms. They develop (briefly) in the updrafts of thunderstorms, building downward to the ground from the thunderstorm base.