I think mostly because the vast majority of business that are owned by people who are LGBTQ dont go around advertising that they are, because they do not want to limit their business to only 1 specific group of people...and also, who cares if they are LGBTQ?  A persons sexual preference is no more yours/my business than what religion they are, or if they are married, or anything like that.  Plenty of LGBTQ people own business's that have absolutely nothing to do with the fact they are LGBTQ.  

After this first occurred, there were several bakeries who stepped up and said they would have no problem making the couple their cake, some even offering to do it for free.  That is what we should be cheering for and supporting - the business's/people that see someone not being treated fairly, and then step up to do whats right.