Some comments praised the old-school Tolkienesque humans and human-like demi-humans (elves, dwarves. halflings, gnomes). Others praised the more modern variety of choices. Some pointed out that even in old school games, players sometimes run odd races like frog-men or sleestak (that last would be me, in Justin's old Vaults of Ur game).
But one person made a spot-on comment. In old school games, it was mostly humans because there were drawbacks to playing the demi-humans. Especially in OD&D and Classic, you didn't have much choice (well, disregarding the supplements and home-brew). Even in AD&D, only humans had the freedom to pick any class, and advance as far as you could go in all of those classes.
So yes, I played a Sleestak in Vaults of Ur. But it was based on the Halfling class in Labyrinth Lord, so limited to 8th level. Yes, there are plenty of demi-humans in low to mid level AD&D play, but if you want to play a high level campaign, better be human (or a thief).
In 5E, there's not much incentive to play a human, other than RP considerations. The variety of races get all kinds of cool abilities. The only real saving grace for humans is the variant that lets you pick a feat at character creation. Since feats in 5E can be pretty powerful, it definitely makes up for the lack of racial abilities.