- Nobody wants this to be closed source. The code is freely available, and you may do with it as you want. The marginal cost to distribute the code is 0, after all.
- The maintainers, as people, don't want to do charity work for companies. Their time is limited, and if they're going to support revenue-generating activities, they want a cut of the revenue.
So even if this doesn't get perfectly enforced (and it won't), that's fine! The maintainers are now free to respond to complaints with "you need to pay us for us to care." Companies that pay get some level of support; hobbyists get the same experience. Only the companies that ignore this warning will see the consequences, and it's particularly effective for reports where the author leans on "but there are a huge number of important users [to me] that are affected." Pay up if it matters!
It strikes me as a pretty clean solution to a pretty common strain of open-source headache, _especially_ as AI-generated code/reports/etc. are on the rise.