If you don't understand why we need to talk about Tim Cook's public discussion of his sexuality then the explanation is actually quite simple.
We still live in a world where gay people are outright excluded from much of what most people consider normal, daily, life. We can't necessarily form legally recognised families. We're tokenised and stereotyped in movies. We're erased and ignored (or worse, merely fetishised) in video games. We often can't simply be ourselves in public for fear of violent reprisal. We're arrested, beaten, raped and killed in countries as advanced and close to us as Russia and Greece.
By suggesting that we should be 'over it' or that as a society we should have 'moved on' it sounds like you're taking the moral road but you aren't. We don't live in that ideal society and so you are only serving to silence the voices we need to make progress towards it. To pretend that this isn't important can only prolong the conditions that allow for massive scale homelessness and suicide amongst LGBT youth. We need representation in business, and in politics, and in sports because those ideas still make people uncomfortable. We are moving on, but we still have a long way to go.