I don't share Eich's views, but he's 58 - the cultural concepts that made it difficult for Tim Cook to be public about his sexuality may be the same thing that makes Eich against gay marriage.
Edit: I can't comment due to rate limits, but a poster below hasn't read what I wrote above and is suggesting I am saying the men grew up in different times. I am suggesting the exact opposite: they grew up in the SAME period/culture.