I think they want you to use their app to earn sats, since with their app you can't skip seeing ads (which with the browser you could with adblock)
I agree this is likely the reason.
However, would appear it is an extra security vulnerability to download the app vs web.
Just thinking out loud: I think one could design the site to require some user action to confirm they saw the ad. Which should address the issue of adblock. Example: Please answer the question before going on to your next lesson.
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