Most users, including myself, provide solutions for fun. Look on StackOverflow; a lot of answers are very involved, and it's a free service. Bountify is like a Stack Overflow for code tasks, with a bonus of beer money if your solution is selected. Bottom line is that it's mostly for fun, as the bounty amounts are trivial wherever you live.
In the US you don't have to declare income under (i believe) $500 from a single source in a given year. So if you earned 5,000 $1 payments, each from a different source you would have to declare NONE of them. If you earned 1,000 $100 payments from different sources you wouldn't have to declare those either.
Personally I'd rather do something for free that benefits the general public than for someone who just seems to be a cheap bastard. Now, if it were coding for an open source project and getting payed trivial wages because the project has no money and devs just need help getting something done... maybe.