I don't know if that makes sense or if it's autistic stuff all in my own head, but just for an example, look at Ollie. I love Ollie (platonically). I think she's amazing. She doesn't always think she's amazing, which is normal, but she's been the one I've seen most often saying in the past things like "I'm not really an idol." or "we're not really idols. we are comedians/entertainers", especially after she's made some raunchy joke that doesn't fit her conception of an idol as pure and perfect.
But I think her zomrades finally convinced her that she's wrong. She produced this amazing tribute to her senpais and hololive as a whole for her 1 million subscriber celebration, and accepted that her fans love her and believe in her even if she isn't always 'seiso'. Ollie's one of my favorites I think because it's so easy to share in her enthusiasm for the people she admires and the love and support she constantly emits. That virtue is appealing.
If they were just streamers, singer-entertainers, that would be fine. I think the title of idol, and the sort of mental framework that comes along with that, inspires and encourages growth as a person. It's also a fun kayfabe if nothing else.
It's also why seeing Kiara on stage at Holofes performing Hinotori with a sea of orange glowsticks was so moving. She was achieving a dream. She could quit tomorrow and that achievement will never go away (though of course I hope she continues and does even more). If you remove the idol kayfabe, it's still impressive and amazing but it changes something perhaps ineffable about the whole thing in a way that would be a little sad to me.