The solution is to learn content that you actually use with some regularity in your life outside of the testing! If you're doing this for education, the payoff might be the exam; if you're doing it to learn things without some particular end goal, you'll have to make your own way to make it worth it.

The language learning app people could try scheduling monthly video chats with native speakers (swapping turns halfway through so it's mutually beneficial) and notice their proficiency improve.