[gary_bernhardt]

I think your argument here could be made about pretty much any activity that humans do repeatedly. The critical difference is that both WaniKani and Execute Program quickly tell you "go home, you're done", so it's difficult to dump hours of low-quality time into them. Whereas advertisement-driven platforms are incentivized to retain your eyeballs for as long as possible, as you pointed out.

[asutekku]

The thing is, if your product is a subscription then maximizing your engagement in a way that the users will stick longer and pay for longer is not a counterexample, it’s just adapting the engagement to fit your business model.

[taberiand]

It could also be seen as adapting the business model to fit the process.

Essentialy, the goal was to sell a product that guided users to learn in the most effective way possible. The learning model is spaced repetition, which requires users to use the product over a long period - therefore the best way to sell it is as a long term subscription.

If the best way to learn was to cram as much as possible in as short a time as possible, then maybe the product would be sold as a bunch of individually priced courses paid in full up front.

As long as the product is fairly priced and provides a valuable service, there's nothing wrong with making money as effectively as possible with it.