Well in general it's easier to fit into "ordinary society" because of the nature of being bi. For gays and lesbians there is kinda a necessity to being involved at least in the past with movements or social groups due to the struggles of dating. There aren't that many gays and lesbians in the world and because they are only attracted to one sex they have a limited dating pool and need to find that small pool. For people who are bi it's still very plausible to forgo this and just integrate into the hetro dating culture which most do.