The problems with aggregated payments go far beyond just ensuring someone can pay hosting and card processing fees. Who will take chargeback risk? Handle KYC for payouts (especially since many garage bands won’t have business entities)? Handle fraud at scale, including fraud rings using your service to validate stolen credit cards?
Centralizing payments requires human monitoring and capital cushions. With services like Stripe this can be cheaper, but still requires nontrivial resources.
The "publisher" takes all of the financial risk. That's part of the deal. I would never use a website that said "you pay us, but if you have payment problems, you have to take that up with the product manufacturer". The aggregator has to take enough off of the payment in order to insure their business, just like they have to take enough off of the payment in order to afford any of their other capital (salaries, utilities, rent, etc).
I'm assuming you have doubts about the practical feasibility of charging "that much". But it has, historically, been one of the best cost-to-compensation models ever created, with entire industries being built around enshrining an ever-more predatory pricing structure that funnels more and more of the product profit to a small council of investors.
https://www.candyjapan.com/behind-the-scenes/candy-japan-hit... is an old (2015) but still relevant illustration of this.
Centralizing payments requires human monitoring and capital cushions. With services like Stripe this can be cheaper, but still requires nontrivial resources.