From what I’ve seen with friends that eventually plonk down in the “solidly gay” zone, many first go through a “I think I’m probably bi” stage when they’re still dealing with accepting the reality of the situation. (mind you, at my age, this was mostly in college, and back in the 90’s, so a bit of a different time acceptance wise). They’d been dating the opposite sex, and that definitely wasn’t right, and they’re attracted to their own sex, so… middle stage “bi” right?
Unfortunately, I think this lends a lot of (especially older) gay people to view bi people as “not fully committed” or thinking that they somehow aren’t able to move past some developmental stage to being a “true” gay. Seems like both sides of the rainbow are just as guilty of seeing human sexuality as black or white and not a spectrum.
and semi-related: one of the funnier bits to come out of the whole Jeff Foxworthy “redneck comedy” crowd (Ron White):