I've kind have noticed over time that a lot of new artists tend to gravitate towards drawing lewd or fan servicey artwork more so than the past were you saw a lot more kawaii~ stuff. I think this might be one of the main reasons, touhou is a very old and busted series from the 00s that while having very great character design, it just doesn't really lend itself as well to the tastes of men and women that want. need. MUST, goon. I think this is because where as a lot of art online was drawn out of passion, and the skill ceiling or standards also seemed quite lower when we consider how a lot of web art/flash art used to look like, now a lot of art is drawn for profit and commissions, more so than before. Thus, since more artists are drawing more NSFW stuff for money, they gravitate to drawing a lot of these horny gacha characters. Another thing to consider is the fetishization of young female characters in the western otaku community has become a lot more taboo, even for stuff like JK's and because normies look at cute touhou characters, regardless of the age of those characters, some really ignorant people just screech "PDF FILE!!!!!", so there is also an incentive to steer towards characters that are more in the "safe horny" sphere, and yes I do hate these twitter terms.
Another thing to consider is that Touhou just isn't the hot, vibrant community it used to be, its not this craze sensation that possesses its fanbase, honestly touhou kind of doesn't feel all that special anymore with how popular it has become, how diluted its core fanbase has gotten. I'm not surprised artist would migrate away from it just out of boredom alone. It held its spark for a very very long time, but it wasn't going to last forever, the internet just isn't what it used to be. Japanese otaku culture was insane, novel, and fun, but that was from the 00s.