And why can't you get your ball back when you hit it into a shallow creek??
I suppose that you think of Swilcan Burn at STA #1, the creeks parallel and crossing in CCC and MER and the likes?
The only golf rule on this subject is #6, about speed of play, hardly applicable in single play.
But, for most of these balls, you'd need a ball retriever. You have none in your WGT bag, there's none provided like at St.Andrews in casual play, so how would you get your balls?
Sorry, no chance!
And have you ever seen Tiger's caddie with a ball retriever?
My two Pfennig: Such a detail would have been too much complication in the beginning, so they scratched it. Now it would mean extra programming costs, and finally, how much would a ball retriever cost in WGT's Pro Shop?