Because it's not based on sexual orientation. Nothing about being oriented to same-sex attraction includes the idea of the *event* of a wedding (that is, someone can be attracted to the same sex and not engage in the event of marriage). There is nothing about who they were that precluded the service; it was about what they wanted to do. And I think the "poor" people are a bit overemphasized here. They were possibly looking to sue, and they had plenty of other options. I agree that in non-monopolized situations, business ought to have the right to choose which *events* they will participate in.