You have to extract 80 calories of heat from each gram of liquid water to freeze it regardless of the current temperature and pressure of the air. And it takes an extraction of a whopping 540 calories per gram of water vapor to turn it to liquid, again, regardless of the temperature and pressure. That heat has to go somewhere! We think of hail as a massive exportation of coldness from the cloud, but you can't get coldness somewhere without putting that heat somewhere else.

That heat energy that is somehow extracted is going to change the characteristics of the cloud. And there are real physical limits on how much time and energy it takes to transfer that heat somewhere else in the cloud.

Your icemaker has a basically unlimited supply of moisture and perfectly stable conditions for making ice, and once its reserves are gone, it cannot supply a rapid flow of new ice. Even if a cloud had an unlimited supply of moisture and perfect ice making conditions, it also cannot supply a rapid flow of new ice once the reserves are gone. It turns out that it is really expensive in energy terms to make ice out of water vapor, and so on energy grounds alone we would expect hailstorms to be short.