Because wearing pink shirts really is very fashionable nowadays, though there still are some people (in America?) who think that the colour is reserved for gay. Ah well, I guess one should not give a shit about the opinion of a person who judges one's sexuality on the colour of his shirt...
I've have never met with such opinions in Europe, so maybe it's just another brilliant american idea ;-)? (just kiddin', we all know that idiots are everywhere, but why should we care?)