For someone in a stable, salaried job that pays reasonably well (assuming USA level or the better paid parts of Europe), it rarely makes financial sense to accept "hundreds of dollars" for a complex task.
That's due to the amount: "Thousands to tens of thousands" would likely get a different sort of response, assuming it sounded like a reliable offer, not a gamble.
Most FOSS bounties pay terribly if counted by the hour. I'm guessing the bounties came to "hundreds of dollars" for several days (at least) work on the developer's part, because so many other FOSS bounties do? They would have to take formal vacation from their day job to do that work, or extend their working hours to focus exclusively on your issues across many evenings or weekends, at cost to their personal life? They would have to change the way they file taxes to accomodate this payment outside the regular flow of salary? Or, if they work in a job paid by the hour already and with flexible hours, they would be getting less accepting your bounties than they make at work?
The burdens and typically low pay make it a net negative to accept small FOSS bounties, for a reasonably well-paid salaried worker, just on the basis of economic rationality. The psychology of feeling obliged to finish the project after agreeing to do it is just one more burden.
