A lot of people already don't care.
I think the act of needing to make an announcement/spectacle about these kinds of things is stupid anyhow. It seems very teenager to me, and that goes beyond just sexual preference.
Except we still live in a world where even your family can be willing to sever their ties with you over it. It can seriously impact every relationship in your life, because far too many people still don't have any clue how to "deal" with gay people. Likewise, it can take some people years to come to terms with the idea that they don't fit the life that our society (not to mention their family and friends) expects of them. The conscious decision to say "fuck it, this is who I am" and do what will make you the happiest...that would be a pretty big deal, I imagine.
Anecdotal Example: I knew a guy, we'll call him Paul, back when I was really active in the Masters of the Universe fan community. He's gay. Had been living "out" for years - had no problem discussing it on the boards, brought his boyfriend to meet-ups at WizardWorld Chicago, even had to quit the Chicago fan club because his ex-boyfriend was one of the leaders. It seemed that he was out, of closet...except he wasn't entirely. His parents didn't know about his sexuality. He felt the need to conceal this pretty big portion of his life from them because he didn't know how they'd react. It wasn't until he was diagnosed with cancer, I.E, faced with the prospect of death, that he decided he needed to come out. He couldn't be worrying about hiding his boyfriend from them while he was undergoing chemo and in need of all the support he could get. Now, I only know the short term story but it did have a negative impact on their relationship. They looked at him differently, even though they were accepting of him and supporting him as best they could.
Now imagine that same warranted uncertainty, but about everyone you know. And ratchet it up the further you move away from the big, affluent, liberal areas of the country. Do you see where maybe coming out would feel like a huge deal to a person, and why they would treat it as such?