It was also easy because gender-noncomforming people didn't explicitly make an identity out of gender-nonconformity. They weren't "The GNC™". They were lots of other types of different and non-conforming. The boys with long hair in the 70's (earlier? I wasn't alive then) didn't to it for the twitter-likes, for some reason. Punk girls didn't ... well, it's in the name, isn't it? And that's just really really obvious ones.

Nobody understands the word "nonconforming" - or of course they do and have set out to deliberately morph it into yet another form of conformity. Non-binary is the complete opposite and it must be by design.

I kept saying "they" when I don't conform to the "male gender" (ugh) either. Never have. No, I've never worn pink, or painted my nails, or really done any other girly shit (sorry, girls, it's not shit, it's only "girly shit" when it's so forced). I'm just not manly. Non-conformity is not the opposite of conformity in the sense of "If not M then F else Error". It's not a third gender, it's not non-binary just because it isn't "either", it's not conforming to standards and stereotypes.
But I said "they" because I too don't identify all that strongly with GNC, I just am - or at least share some select experiences with "truly" GNC people, if there is such a thing. LOTS of people are thankfully gender-nonconforming, and most of them are, ironically, "normal". Because it's not a badge to show how different and unique you are - it's a shared experience for people who realize that we are human first, individuals with wants and needs that don't conform to the 4 and a half strict lines of thinking we grow up with, just based off of sex.

That sounds like made-up esoteric nonsense, but it's part of the reason why it was so easy to co-opt the GNC label. Gender non-conformity was accepted surprisingly quickly. Dressing a little different, or working certain pointlessly-gendered jobs, or staying home as a dad, or many other ways to live your life aren't widely shunned and belittled by absolutely everyone.
And that's where the TQ+ struck. Nobody really cared, in the good sense, so it was an easy term to snatch up, and so juicy too as it contains the word "gender". If it revolves around gender (not realizing that it doesn't), it must be able to be used to make the straights uncomfortable. Knowing how little it takes to accidentally not conform to gender-norms, it also casts the widest possible net to catch many people, especially young people, and convert them to hardcore gender-identity. Why wouldn't you be interested in gender-identity? You are gender-nonconforming, after all.

I mean, even in this subsaidit, many people don't seem to realize that the nonconformity isn't targeted at your gender, but the idea of gender at all. The terms "masculine woman" and "feminine men" irk me a little. They're not wrong - we can attribute certain physical features to femininity and masculinity. It's a bell-curve, right? It's how the "gendered brain" was debunked - gay men don't have women's brains, they just have things in common that are more often found in women. Tall women aren't men. Physically, masculinity and femininity are - sort of? - a thing.
But gender is a social construct. If you make a choice in fashion or behaviour (and it is a choice, as products of social construction aren't innate; God didn't make women's jeans), you're still conforming to gender - the opposite gender. I'm not saying Don't, I'm not saying it's all wrong - it's very often not even a real choice as we only have two dumb "man or girl" options - the belittling of the woman in that example is deliberate and I'm saying it was marketing's idea, not mine. Because that's what they do. That's how they get you and me to conform.