They’re two different descriptors of two different things. Some Drag Queens might be Trans, but not all Trans people are Drag Queens. Infact insisting Drag Queen is (or might be, or can be) a descriptor for Trans, just as Trans people and not in terms of their participation in drag, is to hearken back to be point where it was specifically a slur/negative descriptor for gay men. If some one’s personally gender identity is “Drag Queen” that’s fine, but they identify as such with the full knowledge of what that term connotes. Which is, for the most part, a particular sort of performance based persona who’s gender often (but not necessarily) is different from the gender of the separate person who depicts them. There’s an inherent bifurcation of identity in the concept. Some one’s drag persona is “a person” in the sense of radical theater/never breaking character performance art. In the case of a drag queen that persona’s gender, and gender identity is female (typically, you could however have a drag queen persona that was trans-female). Not “drag queen”. The person depicting that persona, isn’t required to (and typically doesn’t) match the gender identity, sexual orientation, or even race, age or anything else, of the character they portray.
So you get what I’m saying? Its complex performance based subculture built around assembling multiple personas each with their own complex identities. Those personas exist both on stage, and off. Each personas individual gender, identity, orientation etc is “real” in the radical theater, all life’s a stage sense of real. But they don’t by necessity say, or determine, anything about the complex identities of the people who create those personas. Though in practical sense they often do. There are trans people involved in drag. I’m sure there are non-trans people doing drag who’s personas are trans. I’m sure there are some people who are there drag persona. In a very real, non-bifurcated performance way. Hell if I remember correctly there are at least a few non-human drag personas. Anyone who might identify primarily or exclusively as “Drag” with no other descriptor is going to be pretty deliberately referencing all that. In less complex situations if I were to simply start referring to any or all Transgendered people as “Drag Queens” I’d pretty well branded as a bigoted asshole. Because yeah that shit can still be (and is) used as a slur. I would be diminishing trans people (and specifically trans women) to nothing more than gay men playing dress up.
OTHER THAN THAT Transgender was not (or at least isn’t currently) intended as an umbrella term for people with non-standard gender presentations/identities. It pretty specifically refers to those people who’s gender presentation and identity has TRANSITIONED (or is otherwise at odds) from their gender of birth (and typically to the other end of the gender binary). Terms like Queer, GenderQueer, GenderFuck, Non Gender Conforming, and catchalls like LGBTQ on the other hand are intended as umbrella terms, or more broadly inclusive specific terms to refer to the wide breadth of people who’s gender identity and sexual orientations do night line up with expected gender norms.
Anyone can use such terms to identify themselves, or to build new identities around. For whatever reason or in whatever way. I don’t care. You can identify as a Vienna sausage for all I care (though I might think its a bit rediculous). I don’t think anyone who isn’t a crazy bigot really does. But such terms do have generally accepted meanings, often quite important ones. And we need to know and understand those meaning so that, for example, people don’t mistake a news article’s use of the term “drag queen” as a nasty, outdated, and negative way to refer to Trans people when what they’re writing about is Drag as a performance type and the people who do it.