Another similar question is why didn't GMac hit a provisional when he snap hooked that shot into the gorse? There is no way that ball was ever going to be found.
After you just hit a shot that ugly would you really want to step up and hit another one right away? In his case, I'd probably want to wait a few minutes, but I probably hit more snap hooks than he does
Also, had he done so, and put the ball up on the green close with a chance of getting a par out of the situation, wouldn't it be quite the disappointment if a fan or marshal found the ball and he was forced to play the shot a third time under the unplayable rule?
This brings up what I see as a problem with the rules, certainly as applied to professionals playing with a gallery and marshals. He doesn't have any way of abandoning that shot. The ball was either lost or unplayable, and he would have to play again from the same spot in either case. Since the rules for a lost ball, unplayable, OB and water all allow the same stroke and distance option of replaying the shot over again, there ought to be some sort of declaration under the rules that you are abandoning your ball without regard for whether it is lost, found but unplayable, OB or in a water hazard. I can't see any case where being able to do this would give one any advantage over the current rules.
Just for the hell of it, I have to mention the most creative and hilarious use of the unplayable rule I've ever seen. One of the courses I play in the area regularly has a hole with the green cut into a hillside. It looks fairly flat due to the location, but actually has a severe back to front slope, particularly in the front of the green. I was playing with a couple guys who were playing a match against each other, and on this hole one guy has a three footer from above the hole. I know very well that you can't be aggressive in any way with that putt, as a miss will degreen about 30-40 yards down the hill and leave a very tricky pitch to that front pin position. He hits it firm, it lips out, and rolls all the way down the hill. Without missing a beat, he says "that's unplayable", and places another ball in the same spot, and after a quick objection from his friend, and me agreeing with the guy that nothing prevents you from taking an unplayable lie no matter where you are, he makes the putt, this time dying it into the hole as he should have the first time. That was an amazingly smart move, as the odds of getting up and down from there are pretty long - if you are more than a few feet short of the hole, you will be playing the same pitch shot again, so the odds were good he would be left with a downhill putt longer than the three footer he had on the replay.