Does it actually make that much? For starters, her dad was saving the money ever since it could be open to ads, which is why it was a lot when Bocchi got the money. And I don't think that the ad revenue is that much, especially when you consider that her content is mostly covers.
Also, she is even posting as often now that she is in a band. She did seem to almost forget at their school festival.
She makes enough that between her channel and Kessoku Band being on the rise, she is probably the closest to going pro of any of them. Also, eventually, people are going to figure it out and she's going to start getting cross-pollination between the two fanbases.
The other thing to remember is Bocchi is actually written as absurdly talented as a guitarist; she basically carried Kessoku Band through their first show, and the number of subscribers she has on her YouTube channel is VERY high for the space she's in. She has the chops to go pro, and things are starting to move in that direction.
...which is why it's funny she's super worried about it, because she isn't herself aware of the fact that she's actually very good.