Another important discrepancy in the concept of 'sexual orientation'

The West defines 'homosexual' as someone who has exclusive sexual attraction for members of what they call 'same-sex'.

Now, if we agree that male sexuality is not divided between homo and hetero but exists in a continuum, with let's say 5% people are exclusively into men and 5% are exclusively into women, and the rest are somewhere in between. Then what is the rationale behind separating from the rest, the 5% exclusively into men as 'homosexuals' and classifying all the rest as 'heterosexual'. 

By same standards, a 'heterosexual' should be a person who has exclusive sexual attraction for members of the opposite sex. And that should, if there are no social pressures to identify themselves as exclusively heterosexual, amount to just 5%. But is not what the forces of heterosexualization want people to know.