Could be social contagion (there’s no doubt in my mind that trans amongst young/teen girls, especially the ones that have some kind of intervention, is a social contagion though), but it could also be that they’ve grown up in a very online world where everything straight is somewhere between boring and evil whilst everything LGBTQEtc is amazing, brave and deserving of attention. So the rational choice when asked is to say that you’re some flavour of LGBT. The fact that they’re apparently not saying just gay or lesbian but instead they go for BTQetc seems to me that because no one’s checking they can continue their straight relationships whilst claiming a special identity. It would also be interesting to see the sex breakdown of the people answering non-straight, I have some suspicion as to how that would look.