FOSS is basically volunteer work. Even many long-running and popular projects never earned a sat.
Most people won't pay for things that are free. Because they're free. They're seen as presents.
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And even if you have some sort of mid-term financing plan or financing promises, you still have to do a lot of work up-front, to have enough to show potential investors, customers, and patrons.
That makes it like a business, where you invest time, effort, and money into it, without knowing if it will ever generate enough returns to cover your costs.