it's basically what we're probably seeing: and it's not "social contagion" per se

as we walk around life we classify things we see by categories we've learned: some of these are cultural--"blue" or "blue-green," "gay" or "top/bottom," but they're describing the same THING

so around 2015 you get this new category, that 1. says you don't have to have an overwhelming urge to swap sexes and 2. has been iterated to a cohort who can spend up to a decade hating the inevitable changes caused by getting older than 10 years old, treating them as an outside imposition on their bodies, as society forcing its norms onto them against all their will--no wonder a mushy, non-dysphoric attitude proves so attractive to a certain group of people aged 17-22