Doesn’t the term “gay and lesbian” include bi people as well?

No it doesn't.

While many people use “gay and lesbian” as an umbrella term, it really is inadequate to describe the diversity of the LGBT community. Gay and lesbian are identity labels that describe people with exclusively same-sex attractions. This means they are attracted to only one sex, which is something they have in common with straight people. Bisexuality is obviously quite different because bi people’s attractions are not limited by sex.

One of the bisexual community’s greatest challenges is lack of visibility. It leaves people feeling isolated and alone. It is disrespectful and dismissive to erase bi people and leave them out of the language and conversation. When ostensibly LGBT organizations omit bisexuality in their names or programming, they often do so thinking that bis are a small fringe group. Ironically, when they do that, they explicitly fail to meet the needs of the largest single group under the LGBT umbrella, as bi people far outnumber the total number of gays and lesbians. Not to mention that the number of people with bisexual attractions/behaviors who identify as straight, gay, or lesbian is larger still.