OSX got its market share off spoiled 20 year old college kids getting their parents to buy them overpriced trendy hardware. I have a 15 year old and 13 year cousin who each have a macbook because its hip.
But besides the hip factor, OSX succeeds because it is the default on Apple products, where Windows succeeds because it is the default on everything else. When average Joe buys a pc, they go to best buy, and every single device has Windows on it, so they use that. They don't know any better and would never fathom installing an OS, and if you show an alternative to them it breaks their minds because it is universe breaking that Windows isn't the computer.