To devil's advocate in a different direction, most projects aren't setup to actually do anything with donations. They could be, like if they had a stable income source they could hire people full time as a job rather then relying on volunteer time. And some of the larger projects are already at that point, and so maybe having more money would allow them to expand the team further. And some projects have a particular goal they're trying to fund, like an external security audit, or some kind of certification process.
But for most projects, sporadic donations are like "hey cool, I guess. I'll go out to dinner tonight" gifts of appreciation, because up until they become a solid full time wage, they're not a solid full time wage. And once they are a solid full time wage, any further donations are like "hey cool, I'll go out to dinner tonight" until they're big enough to be a second wage 😛
I'm not saying we shouldn't donate stuff, gifts of appreciation are still appreciated, I'm sure. But they don't produce output.