Because owning a MAC product is akin to driving a Porsche. It's a status symbol. If Apple is good at anything, it's marketing.

MACs started out as being for people in the creative industry because they run the graphics programs better. I'm not sure if that is true today, but my post-secondary education conditioned me to believe so. That is why I still use one. But hopefully I don't "boast" about it in the manner you describe.