This viewpoint seems to be prevalent, and I can't help but to disagree with it. To me, it is a matter of Occam's Razor. Rather than some insidious plot to relieve fools from their money by deliberately removing monsters from the monster manual for use later...I find it much more simple and much more likely that there were a crapload of monsters, including iconic ones from decades of game history, cool ones they felt needed a time to get in the spotlight, and new ones they wanted to throw out to try the waters, and they had to draw the line somewhere. Where they drew the line is arbitrary in the end, the point being that they chose a certain book length, filled it with monsters, and then stopped adding more monsters.
