Explain it to me please?

One of the concepts I just don't get is 'bicurious'. I know what it means - a straight identified man is advertising for sex with another man - but the term provokes me. By the time someone is advertising for sex - the usual times I've seen it - they're no longer curious. They're ready to take action. And what they are is bisexual, not heterosexual. Please tell me why someone wanting to have sex or date or something similar is only curious?