Most people would prefer an excellent language learning app to simply be available and ready for them to use, rather than having to come up with how such an app could best work, and to get an AI to implement it by themselves, and having to iterate on that. Just like most people simply want to buy nice clothes, and don’t want to become fashion designers and managers of a clothing factory. So far it doesn’t look like AI is making the former (readily available excellent apps) more widespread.