I think they chose breast cancer over others because it has a relatively high success rate with early detection and treatment. Therefore awareness and money raised can make a big difference. This is pure speculation on my part, but...
I ran into a buzz saw at school with the "I heart boobies" bracelets. My mom survived breast cancer. I was pissed when I watched kids buy them and wear them for shock value. I know the money goes to a good cause, but these kids were not interested in carrying UNICEF boxes or raising funds for the CROP walk, etc.
I guess my point is, as long at it is not too tacky, I'm okay with it.