Sounds like they suffer from the same illness as dating apps: Being successful means users graduating and leaving the platform.
"Why settle for 3 years when you can milk people for a lifetime? If it takes 10,000 hours to master something," it doesn't but they'll likely use that meme, "and you plan to spread that learning over 72 years, they must not spend more than 22 minutes a day actually learning anything! The rest of the day should be adverts and retention."
I can hardly remember any of the Esperanto, I never even mastered the Arabic alphabet let alone basic phrases, and actually living in Germany rapidly revealed how mediocre it had been at teaching me German.
I stopped at a 2500 day streak, shortly after one of the big controversial UI changes.