It is a matter of time and random chance.
Is there any reason for us not having a Jewish, Polish-American, or Italian-American President? We might have had a Greek-American President if Spiro Agnew weren't corrupt or if Mike Dukakis had run a better campaign.
And, yes, someone ignored the distinction between a closeted homosexual and someone in the open. I would not vote for a closeted homosexual because such a person is a liar (if it is my choice, I would not vote for a 'closeted' alcoholic either). After Trump, integrity will matter as it has not before. Out in the open? No trouble for me.
Is a closeted politician a liar or someone forced to hide a significant part of their identity because of an homophobic society? Of course, if that person lies to their husband/wife, it's different but I have no trouble with a politician who is single and doesn't feel comfortable in disclosing their sexual orientation.
And unlike a closeted alcoholic, the person's homosexuality/bisexuality won't affect their capacities and how they do their job.