I suppose I've always been shit at explaining things and trying to would just drive us further off subject. Either way, the argument of what is homosexual or not beyond the hard definition of two of the same sex having sex is purely subjective, and I feel the need to defend one's perception of what defines homosexuality beyond the hard definition to be a matter of futility as it is not objective and therefor merely a statement of one's opinion, which doesn't really matter to anyone but ourselves what our opinions are. Either way, back to the matter at hand.
I think you just left out the part about a lot of men still associating gayness, or really anything even remotely thought to have connection to gayness, as emasculating. Doesn't help that most people think of bottoms when they think of a gay man, and that even singular actions somehow overpower long time trends;
You're some 2 meter tall giga chad looking absolute unit. You help others in your community and charm most women you come across. You've fucked half of the single women in your town. Only thing bigger than your charisma and fat bank account is your cock. Yet if you were to kiss another man once, a lot of people would start to question their masculinity in this situation, and they would probably also try to compensate in the future for this single action to prove/reassure to themselves that they're not gay.
You did one thing associated with "gayness", and now you constantly think: "Am I a man, or am I gay?"
(Obv this is exaggerated and irl it's usually more subtle...)