Lord, dude. Yes, there are straight men who never, ever, ever think about doing anything with another man. That's totally fine and totally acceptable. Nobody is saying that it's not. But just because someone has dabbled, or has been bi-curious once, doesn't mean they're bi-curious for life.
When I look at a dick, I'm not turned on by it. But I'm man enough to admit I have scoped out dicks before. If you haven't, that's great! But I have, and you probably think that makes me gay. And your hyperbole is showing. One can be curious about something and not want to fuck another guy. That's a completely different subject. Yes, if someone is having ongoing desires, thoughts, and experiences, then they're clearly not straight. But going to the well once or twice in your life doesn't make you automatically bi. This isn't even a new concept; why do you think so many guys have experimentation stories? Best buds from junior high, or a drunken fling at college?
What works for you, works for you. But your experiences are not universal and your attitude is myopic. Guess there's a whole shit ton more bi guys out there than is reported, apparently, under your theories.