ECO codes are generally sequenced from the least popular openings to the most popular. This means that code A covers openings which are less popular than code E, code A0 is for openings less popular than code A9, and code A00 is less popular than A09. This is only a rule of thumb. The coding classification was devised in the 1970s and opening tastes, like fashion, have changed since then.
One thing hasn't changed, and probably never will change. The openings classified under A00 are the least popular of all openings. Why is that? First and foremost, it's because chess is a game of logic.
Chess players don't play to pass the time, although chess is an excellent source of amusement. Chess players play to win. The most popular first moves are those that offer White the best winning chances.
The logic behind chess dictates that, other things being equal, control of the center and superior piece activity are advantages. These are such big advantages that they are often sufficient to win the game.
The initial moves classified under A00 either neglect the center or neglect piece development. The worst of them neglect both.
