Her main audience were parasocials in love with her.
This is because that's who she raised. Her intimate streams, her asmr, her kisses after every stream, the way she teased her fans and baited them to tease her back.
She then goes and calls out parasocials.
She also brought in politics to vtubing with her out of nowhere trap arc, even if she backpedaled, the damage was done.
Her game choices went to shit, she went from a variety of cool content like GTA, hitman, lol, vallhala, nekopara, random minecraft mods or indie games to GACHA every week, then 2 gacha streams per week, then 3 gacha streams per week, at one point 50% of her weekly streams were some sort of gacha
Finally of course, males
A vtuber whose audience is composed of more GFE fans is going to suffer more from male interaction. Girls like Selen manage to keep a certain distance from guys and makes their interactions with them to feel like just a guy with another guy. But not Finana. She let males flirt with them often.
There was also that time she planned and teased and built up a big collab with Pomu, her genmate with the best chemistry with her, the pufferfeesh collab, with unique cute yuri art.
And when the day came there was a guy in there between them and ruined that mood entirely. She then confesses she brought him there in secret.
This made her lose the trust and support of a lot of fans.
The final nail are the leaks that she made a server with some of her fans and has been interacting with them privately. How does this affect the rest of the community? Of course, it doesn't. But fans don't like the idea of some of them having special access to their oshi, specially fans with a GFE leaning.
Finana always had a history of doing and saying extremely retarded shit but it was often just silly stuff and she's cute so she got a pass. But as she did stuff that revealed her lying nature people lost trust in her and the cute pass got weaker and she came under stronger scrutiny, and the shit she did/said got worse.
The whole shit against Zaion SHE GASLIGHTED ME SHE GASLIGHTED ME wouldn't have been so bad for the old Finana but for the current Finana it's another case of her being stupid and saying shit she doesn't need to.
Basically, she did a ton of shit that turned off her fans and she lacks any other appealing traits that could make up for it, she lost her audience and couldn't get a new audience or recover them or retain many of them.