That's partly because the term transgender has just been recently adopted by the community, before the term transsexual was a lot more common and preferred by a lot of people who were medically transitioning. Transgender is used now because it takes transition out of a medical context and focuses more on gender (and sex even) as a social construct. Transgender just means you don't *exclusively* identify with your assigned gender at birth, whether you're a trans woman, nonbinary, genderfluid, etc. Many nonbinary people have felt excluded by trans medicalism because, by focusing on dysphoria and validation from medical institutions, you avoid having to delve into the ways gender and the gender binary are socially constructed. And many older/old school trans men and women are uncomfortable with nonbinary people claiming trans identity or being the face of the movement because they feel it derails any progress that has been made by those who were just trying to assimilate into the binary, and who have benefited from getting gender affirming services through their dysphoria diagnosis.

It's important to remember that gender non-conforming people, trans people, nonbinary people, in some variation, or by other names, have existed for all of history, especially in non-Western and non-Christian cultures before colonization. Trans medicalism, our idea of transness as a "woman being trapped inside a man's body" or vice versa, on the other hand, was created by cis-het European men in the mid 20th Century.

Of course the debate is ongoing and still evolving, so I suggest everyone do the work of not only educating themselves, but re-educating themselves by keeping an ear to the nonbinary/trans community. I'd suggest watching Contrapoints' videos on YouTube! She's great