The gaming community leans towards being white and male, so when Magic began, there was a major carryover, resulting in a mainly white male player base. Let’s talk for a second about social pressures. When people have friends that play, they are more likely to invest more time and money in the game, so that leaning has mainly stayed true, with the Magic community still leaning towards white males, though there is definitely a growing number of minority players.
So, though there are no credible statistics, when Magic began, the player base was probably significantly more white and more male than it is now. But why should that count? The best players are basically the players that have spent the most hours playing, with some element of luck. It’s a generalization, but it’s mainly true.
So, if white males have the most friends that play Magic, then they’re more likely to invest the time and money needed to enter the competitive scene, because being better at the game brings them more than it would if you had friends that didn’t play Magic.
I'm hoping that soon as the player base gets more and more diverse, the competitive scene reflects that change.