The main problem as i understand it ... is lift. You can only lift water under a vacuum to a depth of 30 feet or so before air bubbles start to develop. You lose your prime.

I suppose you could think of it this way. There are gasses dissolved in the water. Lowering the pressure causes the dissolved gasses to come out of solution. It's kinda like opening up a bottle of carbonated soda. Crack the cap, drop the pressure in the bottle, and all the little bubbles form.

Same basic idea i guess.

That's the virtue of having a submersible pump at the bottom of the well.