Why are bisexuals part of the gay and lesbian community and not the heterosexual community?

Not all people of any sexuality belong to the the same community. For instance, many heterosexual people join the LGBT community in that they fight against bigotry and persecution of gays and lesbians.

Likewise, some gay people and bisexuals choose to avoid same-sex relations (even if they can't avoid the attraction), and do not become a part of the LGBT community. Many Republicans who hide their homosexuality have been the source of the most hateful rhetoric against homosexuality.

Obviously, as bisexuals face the same persecution as gays and lesbians when they are seeing someone of the same gender, it is natural for majority of them to join the LGBT community.