Well, the majority of people want to play games or get cheap computers with a lot of power. They then, generally, go for PCs.
Other people who want beautiful computers with a lot of power, who want fast, efficient and virus-free computers with perfection to the system design then go for Mac.
There are lots of children in the world and people who want to play games and pay for cheap computers, therefore, theoretically, windows sells more for this reason. After everyone sees that statistically microsoft sells more, everyone designs everything for windows. As stated before, if Macs make their computers with more and better capability with games and their prices cheaper, Mac wins.