> The .NET Foundation accepts projects that use permissive licenses within that set [of OSI-approved licenses].
> The board clarified that projects in the Foundation must use a permissive OSI-approved license and that projects would all be treated the same.
Per the linked article https://sixlabors.com/posts/license-changes/
> Previous attempts (sponsorship, support license) to provide a sustainable income to ensure the continued development of the Six Labors libraries have not proven successful, yielding less than a few months of developer income over a period of several years.
It sounds like James' monetization efforts were unsuccessful. The new monetization approach and relicensing is not considered compatible with the open source nature of the dotnet foundation. Whether the new approach works remains to be seen, but it likely burned a lot of community goodwill.