Why aren't there screw-based cocking mechanisms for crossbows?

I’ve been looking at crossbows, and have noticed that the mechanisms used to cock them are either cords that you pull with or involve manually turning a crank and winding them back. This made me wonder, why don’t they have a screw running the length of the rail with a sled that can be pulled down the rail as the screw turns. I would think with fine enough threads, the mechanical advantage would be such that a small battery motor in the stock could easily/quietly draw back the crossbow string.

This isn’t the case though, so maybe I’m misunderstanding the physics involved in drawing back a powerful bow. Why isn’t this done?