You are making an assumption here. What makes you think he didn't hear plenty of homophobic comments from teammates in general, so he didn't feel confident they would accept him if he came out?
I've been playing sports my entire life and there're still plenty of anti-gay attitudes being expressed among athletes. I used to make plenty of joking comments myself, failing to recognize that while I didn't actually have any issue with people being gay, I was being pointlessly insensitive to them without even knowing it. I don't do that anymore, but lots of folks still do.
So maybe what really sucks is that society, while improving a lot with the current generation, is still not very accepting of people who are different from us?