DuoLingo recently changed to the policy of awarding the bulk of points for translations only after a translation has received a certain number of good ratings from other users. For this to work, they need to pressure users to rate each other's sentences more than they did before. I still get a mixture-- sometimes I am asked to translate a sentence, sometimes only to rate other people's translations-- but I think the latter was introduced when they changed the awarding of points for translations. You can't run a popularity contest without voters, after all. :p