Why is it any different for heterosexuals?
Generally speaking, now, as there are no exact rules or sciences applied- Gay men who are just friends have some
feature of the relationship that makes one unattractive to the other or unavailable. A gay man in a committed relationship
might have a gay friend who respects that relationship and doesn't violate it, same as a straight man and woman. You won't
find two gay men very often who are "just friends" with the type of man they are attracted to, but choose not to act on their
commonalities.
A straight man might be sending the "clearly not interested in a gay relationship" vibes to a gay man. No problems.
Lesbians, well, lets just say that sex isn't near the top of womens' minds all the time and they can be friends with
just about anyone. It is not about sex unless they want it to be.
The straight man with the straight woman as friends- If he respects her mind, that doesn't mean he's not noticing her
body. He tends to think of what sex with her would be like. He tends have fantasies. What lady out there has gorgeous
single girlfriends and truly believes their husband doesn't think about having sex with her. Sure, he never will, but that's
more because he doesn't isolate himself with her on a regular basis.
One exception (to the general rules) would be a straight male who is friends with a group of ladies, or a straight
female friend to a group of males, or a mix. Even here, two of them might start to isolate themselves.
Can you point to another example of where it actually works, yes. But in most of those cases, there is a reason for
a lack of attraction or a family friendship that overrides any sexual attraction.