Touhou was the grand macdaddy for so long because it was a cultural touchstone. Take any rando doujin idea you could think of, then think: i could make up some rando generic whos... or i could use 2hu girls. Boom, plug it in. Instant cache. It was like the 'vocabulary' of the fan-work world.
Nowadays that kind of 'placeholder' status doesn't really exist; or to the extent it does exist, it's attenuated between multiple properties now, with recency impact having a larger influence.
The schizo rrat take would be that these happenstances, if they indicate anything, are simply an epiphenomena of more fundamental subterranean dynamics at play, which are the progressive atomization of modern society, collapse of traditional social technologies that allow the humanoids to connect and act together as singular extended organisms, as it continues it's slide towards a singularity event, events leading to which can be predicted, but events past which which cannot be accurately predicted.
