Earlier quoted context omitted.
It doesn’t have to be that way; learning a language is a long process. I took about 3 years to reach real practical fluency, and I still have to say “what?” more often than I’d like and I still need to learn a ton of more advanced vocabulary. Duolingo unfortunately doesn’t offer any C1 content so I’m stuck using other methods.
Imagine the shareholders saying: "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 could see it as well. For me currently, I’ve completed 100% of the Spanish course, and I’d like to keep learning more, but there’s no more content. I think there’s a lot of more legitimate opportunities they could find, in the way of more content, to keep me coming back. Right now to be honest I just continue using it to maintain my streak, since I’m already fluent. But! I’ve recently started learning Italian, and maybe that way they can get a couple more years out of me.