>>43689131First problem: They don't have a reputation for games or personality that appeals to people, more people latch onto content by association rather than just the raw talent.
Second problem: Expectation Bias. Sora, Azki and IRyS all have very stereotypical idol/singer getups and so the viewer is adverse to check out their singing content due to an underlying familiarity and assumptions about their music. IRyS is relatively big as a streamer, but her songs don't catch on as well despite the association buff because of this reason. Meanwhile someone who isn't known for their singing, like Botan, pulls in a lot of views because their design and content isn't associated to anything we know about music, we expect something different and so check it out.
The idol girls need to take a lesson from Suisei's book and have a few months or a year dedicated to releasing a different genre, IRyS' heavier or slower songs perform much better than her idol/anime style songs. I also think they get a big boost from having plainer or alternative outfits, Sora was somewhat viral when her plainer outfit got revealed and Covers that feature different drastically different styles also do well.
tl;dr if you look like a singer, people are less likely to check out your stuff.
