There just hasn't been as much original Cinderella Girls content recently to drive fanwork. Even the last season of Gekijou is a couple of years old, and of course the Mobage game is shutting down. Meanwhile, Love Live has had two different anime per year for the last bit, between Superstar and Nijigasaki, and they've still got Aqours doing concerts. This year, they've got Nijiyon, another season of Superstar, the Nijigasaki OVA, and the Yohane spinoff — plus, Love Live has always been more invested in teasing their yuri fans.
Now, the U149 anime is hitting this summer, so I expect an uptick in Haru/Risa doujinshi, and possibly Arisu/Momoka; this may or may not be an improvement.