They did do it for a profit motive. Through whatever instincts or thought processes the beavers had, they figured that they would benefit from damming the river. The dam creates favorable conditions for hunting, nesting, and storing food. These benefits are a sort of profit. Money is a convenient kind of profit, because you can easily turn it into whatever other kind of thing you want and you can store it for later use - and also it is convenient to talk about in economic terms, since it is uniform and easily quantifiable. But no one (or, few people anyway) want money purely for the sake of having money - they want money because it allows them to have other things. Food, housing, good conditions for mating and raising their young.

Sorry. The beavers were only in it for themselves.