We have no interest in the Ukraine. This is true. We do, however, have interest the resurgence of Russia as an international antagonist. If we can stop Ukraine from entering into the Russian fold, we can put a kink in the establishment of the Eurasian Union (tentatively with Ukraine, Georgia, and Azerbaijan), which would otherwise negatively impact our economic clout.
Fact is, in an almost totally globalized economy, almost everyone has an interest (either direct or indirect) with every event in the world, whether you like or approve of it or not.