What if there are simply not enough people who enjoy this sort of music enough to be ready to pay for it?
Maybe the problem is not that it is hard for non-mainstream music to find its supporters. Maybe the problem is that non-mainstream musicians are deluded to think they have enough supporters to make a living off their music.
Even YouTubers that produce free content can make a living off Patreon. Even some podcasters can.
There is enough people who enjoy it, however; the proof is that those artists used to be able to make a living through their followers in the past.
The issue is that attention is a scarce resource, and the means to keep it through market formulas and analysis of trends have become way too effective. Artists are now in a race to the bottom where they have to choose between playing the game, and changing their style, message and work to chase engagement metrics, or resign themselves to be drowned and forgotten for staying "real"
Youtubers suffer the same fate. You can see people moving from tech reviews to game streaming and then to music production or vlogging in their search for views. But they (most of them) are more businessmen than artists, and don't feel tied to a message or artistic vision that they need to communicate.
I'd argue that an ideal system should have a place for artistic quality to shine beyond entertainment, and that used to happen, at least to a higher degree than it does now. Which is not to say that everything's worse: the tools to become a creator are better and more accessible than ever (hardware, resources to learn, etc).
Maybe the problem is not that it is hard for non-mainstream music to find its supporters. Maybe the problem is that non-mainstream musicians are deluded to think they have enough supporters to make a living off their music.
Even YouTubers that produce free content can make a living off Patreon. Even some podcasters can.