Tim beat me to it, but I'll post anyway.
1HP decks are so uncommon in the upper leagues, Gold and Platinum, because that's where most of the current player base is. There are more than 500 players actively submitting decks, so once a deck hits 7-8 days old, it loses rating very quickly, and becomes inactive.
Unfortunately, Bronze and Silver don't have that luxury - there are less than 500 players actively submitting decks, so even when decks hit 1HP and lose rating, they don't get eliminated, and instead sit in the rank 350-500 range. This is why you run into so many of them - you've got a ~150/500 = 30% chance of finding a 1HP deck.