If you implement one of the bounty algorithms you get the bounty, but you also get a payment when your algorithm is used. It's not going to make you a millionaire, but if you work in $FIELD_OF_STUDY and want to make a couple bucks in your spare time it might be worth it.

It's also likely that someone who wants to enter $FIELD_OF_STUDY might use one of these as a portfolio piece. You learn-and-implement one of these algorithms to get an introduction to the field, you get a bullet point for your resume and you make a few bucks.