Having a full-time and well-paid job means that open source work is in my spare time, and that time is limited and precious. I don't actually
want to be paid for that. Or have any written or unwritten major obligations to others. The amount I need would have to be a full-time job that pays better than my current full-time job, and that will be expensive.
I've previously worked on large open-source projects like Debian, taking upon many obligations and essentially working a second full-time but unpaid job. That's definitely unsustainable, and I quit for several reasons with this being the major factor. Working like this is definitely not in anyone's self-interest.
Like another poster in this part of the thread, I have tried my hand at open-source consulting work, and I didn't have a viable business. You can't rely upon the sporadic needs of end users; you need something more sustainable, and not every project can support that.
This is coming from a UK perspective, but if you're earning money in anything more than trivial quantities, you need to register as a sole trader or create a limited company. That brings with it legal obligations, and other obligations, like bookkeeping, separate bank accounts, corporation tax payment, company reports and tax returns, personal tax returns and more. That makes for a lot of friction to take payments, and is a huge amount of hassle and inconvenience. But these are all factors in why I don't currently have any intention to make money from open source projects. There needs to be a way to narrow the gap required to make the transition from unpaid to paid work without all of the overheads of running a full company. Maybe there are ways around that to make it an easier burden to bear.