>>5766926798% of them make peanuts and need a side job. These are youtubers; not Hollywood mannequins. Things aren't that lucrative for the idols even at the very top.
Let's look at HoloLive as an extreme example:
Depending on source-estimate, only ~30% of the Superchats actually go to them. Ditto for Memberships. (Anyone who's ever had a consignment job can tell you that's actually generous. Usually you get 10-20%) And they technically 'have' a salary but it's the same sort as tipped employees like waitress where it's entirely eaten up in taxes and you're supposed to live your tips. And, as far as merch goes... some of the girls are unaware they even 'have' merch sometimes, which says enough about how little, if any, of that trickles down to them. Corpos are only really lucrative for the shareholders.
So, to put a number on this, let's go to Hololyzer and look at Kronii just to pick an example.
+ Let's assume, as mentioned earlier, that her regular salary and her taxes cancel each other out. (That's usually the norm for commissioned or tipped employees and makes the calculation much easier.)
+ So, Kronii's median SC ranking is ~¥250,000 or ~1,700 USD.
+ Let's assume the generous 30% cut; 30% of 1700 is 510 USD.
+ Let say she streams biweekly, so 8 streams a month; 510 x 8 = 4080 USD per month.
+ Now, for memberships. The highest number of members ever seen on one of her streams at once was 1890 for her anniversary, which is probably as close to perfect attendance as it's gonna get, so let's just say 2000 is the norm.
+ Monthly membership is 5 USD. So; 5 x 2000 = 10,000 USD monthly from her regular members.
+ Again, let's say her cut is the generous 30%. 30% of 10,000 is 3000 USD.
+ So, we add 4080 from SCs to 3000 from memberships to get an income estimate of $7080 monthly.
+ There's 12 months in a year, so 7080 x 12 = An annual salary estimate of 84,960 USD for Ouro Kronii.
And this, I remind you, is at the VERY top. I guarantee you that no vtuber, not even Gura, has ever made $300k annually. There's a reason why half of these girls still live with their mother.
tl;dr: If you plug the math, the holo idols are turning about the same salary as a mid-tier white collar job. I was making about the same as Kronii's estimate during my own stint as a corpo scumbag. They're not poor, but a far cry from rich.