How do you legally distribute financial contributions? Who will be eligible to receive funding for work on a particular project? Who figures out the tax issues across jurisdictions? How do you become a relevant site representing such projects?
I am not saying it cannot be done. It definitely can, and the more options we have the better. Sites like https://www.opencollective.com are trying. Github has a bunch of new Sponsorship features. They have the audience.
Sites like https://www.libaries.io and https://www.repology.org are building dependency graphs. There are other places which can help to identify the recursive structure you are after.
Fiscal sponsorship entities like https://www.sfconservancy.org and https://www.techcultivation.org, apache.org etc are trying to tackle some of the issues to legally represent projects (and receive donations for them).