If your money making model depends on hoping real hard that a giant megacorp throws you a few pennies once in a while I would argue your whole premise needs a rethink.
But to answer your question directly, artists make money the same way they always did - making art for rich people that appeals to their tastes.
Open protocols don't make for open platforms. Mastodon is "open" yet big server admins are free to block anyone else they don't want, going back to the closed garden model. It is for good reason of course, there always be bad actors, but open or not it's all to easy for organization to use same tools to further their own goals
Couldn't you make the same argument about email? It's an open protocol but anyone can block you.
Even though that's the case, I think email is much more open than WhatsApp or Signal, and a big part of that is the fact that it's a federated open protocol.
But to answer your question directly, artists make money the same way they always did - making art for rich people that appeals to their tastes.