It is mainly a diet thing.......seen it loads in fat little welsh halfbreds, saying that it's difficult to feed every ewe right as you will always get some fatter than others and if their scanned for twins will need the extra feed.
I had a ewe at home that prolapsed very year for three years, each year a little worse til I finally culled her, so I'm guessing once it has happened it creates a weakness which makes it likely to happen again.....
Most commercial folk cull after the first time