I've noticed this as well. I almost wonder if the Mint took extra care to make these nickels as attractive as possible, expecting large numbers of people to collect them for being "Y2K coins"? It was a big enough deal that Cheerios purchased $100,000 worth of Y2K pennies to give away in their cereal boxes.
And, since '00-D is the second most common date after '64-D, maybe they've just been sitting in mint vaults and coin jars until the economy took a bad turn a few years ago?