This interesting clip shows why Skinner's behaviorism ideas of language acquisition in children won't die although they've been repeatedly debunked as total rubbish:
I agree that behaviorism has a lot of problems, and can't account for all of language. However, rewards and punishments can be a big short-term motivator for long-term learning. I have seen young children who would gladly commit bloody murder if they thought it would earn them a sticker from their teacher. People will put insane amounts of work to change their avatar in a learning app or watch a lazily-animated three-second fireworks display.
But of course rewards and punishments aren't the only components of Skinner conditioning: there's also the formation of an immediate, unthinking association between the reward or punishment and the target action. This is useful too. When I click on an answer I'm not sure about on a language-learning site, my shoulders tense and my adrenaline spikes while I wait to be punished with a flashing red "X". Is that enough to make me learn a language? No. But it provides a nice bit of short-term motivation to supplement my long-term goals.