In addition to that, "consideration" doesn't have to mean "money" — in fact, consideration usually won't be monetary on at least one side of the contract (e.g. if I offer you $5 to mow my lawn, the lawnmowing is consideration). If your license requires people to give you attribution, that could reasonably be viewed as consideration.

(IANAL and obviously this comes with the usual truck full of caveats that all legal issues do, but this is my understanding of the general state of US law at least.)