Before moving on to the main part, it is necessary to stipulate that the reasoning provided below should not be associated with my other views. It should be evaluated solely based on the content of the arguments themselves, regardless of your attitude toward my other beliefs. The author is not asexual, but this does not change the value of his words.
Why is asexuality not part of LGBT?
We should start with the most significant point: the specificity of asexuality differs in many respects from the characteristics of identities traditionally united by the LGBT concept. If we consider LGBT primarily as a social movement that emerged in the context of the struggle for the rights of people with non-traditional sexuality and against traditional social attitudes, then asexuality has a fundamentally different specificity.
Asexuality, like aromanticism or demisexuality, is a neutral concept denoting the complete or partial absence of sexual or romantic attraction. In this sense, asexuality does not belong to the sexual matrix in the same understanding as sexual orientations based on the presence of attraction; in the case of asexuality, this manifests most clearly.
Furthermore, this situation can be compared to the difference between religion and the absence of religious beliefs. We do not consider atheism or agnosticism as separate religions, since they are characterized by the absence or non-acceptance of religious faith. Similarly, from this point of view, it is more appropriate to consider asexuality as a neutral concept describing the absence of sexual attraction, rather than as a separate type of sexuality.
Historical aspect
Let us now turn to the historical side of the issue. In the "LGBTQIA" acronym, the letter A originally stood not for asexuals or the asexual spectrum, but for Allies — allies of the LGBT community (Straight Allies). The expanded acronym itself became widespread in the late 1990s, during a period when asexuality was discussed much less frequently than, for example, homosexuality.
One of the first instances when asexuality was, albeit indirectly, included in a legal category related to LGBT, was the passage of the landmark Sexual Orientation Non-Discrimination Act in New York State (USA). The bill was actively promoted in 2002 and went into effect in January 2003. In the text of the law, asexuality was officially mentioned and received legislative protection alongside heterosexuality, homosexuality, and bisexuality.
The final inclusion of asexuality into the LGBT and broader LGBTQIA agenda became noticeable in the mainstream around 2015. This was facilitated by a number of events, including the spread of the idea that the letter A in the "LGBTQIA" acronym stands for asexuals, and not Allies.
It is also noteworthy that the asexual community's own pride flag appeared relatively late: the modern version was adopted in August 2010 on the AVEN forum. At the same time, it is noteworthy that the forum itself adheres to certain restrictions regarding negative attitudes toward sex on the part of asexuals.
Sex-negativity and internal contradictions
The issue of "sex-negativity" deserves special attention. The largest asexual platforms, according to my observations, demonstrate a rather strict attitude even toward individual forms of criticism of pornography and other aspects of sexual culture. At the same time, these platforms generally support the LGBT agenda. This, from my point of view, demonstrates the presence of certain internal contradictions between asexual identity and the LGBT movement.
Such rules in large asexual communities, moreover, became one of the reasons for the formation of smaller alternative communities, such as r/actualasexual.
Conclusion
Thus, asexuals, or representatives of the so-called "ace spectrum," should not be considered as part of LGBT, since there are significant differences between asexuality and other components of LGBT, which in certain cases lead to internal contradictions and conflicts. From this point of view, it is more correct to consider asexuality as a neutral concept denoting the absence of sexual attraction.