You seem not to have read what he said.
Paraphrasing: He believes that he has benefited from the courage and the work of many gay people. And by saying that the CEO of Apple is gay, _he_ can in turn help many gay people who are in a less strong position than he is.
You can easily see how necessary that is by reading some of the posts in this thread.
Sorry but the stock holders to the company he is CEO may think differently and wished he kept his private preferences to himself!