Well, no, because they don't need to. Being heterosexual is more socially acceptable than being homosexual. Also, society assumes everyone is "straight" by default.
I'm not saying that Mika has to shout to the rooftops "Heeeey, I'm gaaaaaay!!!" That's not what being openly gay is about. However, it would be nice that if he were in a relationship with a man, he could discuss it. Seeing as how heterosexual men and women openly talk about their partners and home lives.