The actual reason is that the vast majority of Duolingo users are only using the app because they like to play Duolingo. I don't say this to insult Duolingo use

The actual reason is that the vast majority of Duolingo users are only using the app because they like to play Duolingo. I don't say this to insult Duolingo users, but they're not actually serious language learners. They just really like playing Duolingo and if Duolingo stopped existing, they would simply stop "learning" languages all together.