My thoughts:
I believe the draw is random, BUT, I also believe (no proof, just offering an opinion) that the draw is only for players within a certain range (maybe top 500 or so). Many people will just take the free ball, and go blast away without aiming or setting club, ending up with a 6-700+ score. Why would WGT even consider these people, when it's obvious they aren't even making a lame attempt. This is a stretch as far as opinions go, I know.
I generally use a promo ball, and I will still restart if I hit a way-off shot. Maybe it's just that some players enjoy trying to do their best.
Has anyone ever won 500 credits?