His homosexuality is terribly unimportant. By the time of his death, he was in a dry spell and had made no significant breakthroughs in several years. His homosexuality did not help him find his discoveries, and his suicide probably did not deprive the world of much in the way of additional discoveries. He did what he did, and he contributed quite a lot. The homosexuality is an insignificant detail.
Turing was a true genius whose accomplishments had a profound effect on world history. Therefore the details of his character and biography are of interest. Obviously the fact that he was homosexual and was hounded by the authorities because of this are very significant details of his character and biography, as they would also be if true of any other famous person.