You're describing exactly what happened to me. In elementary school, I read so many books that I would win free books each semester. We had mandatory reading quizzes each month for books of our choice, and high scorers would select a few books to keep from a big spread. I would read larger, more complex books from the 3rd to 6th grades, as they would net me more reading points than simple books. Thus, my (competitive) book reading habit would feed into reading books I received for free, which in turn could be used to take extra quizzes to win more books.

Then, middle school happened. I was stuck reading books I didn't care for, covering topics I was already familiar with, and writing analyses that I was already capable of forming within my head. This continued through high school, where I found that I was so disillusioned with narrative literature that I much preferred non-fiction and educational content. I fell out of love with reading, and I don't think I've finished reading a book on my own time, out of enjoyment, in almost a decade (excluding textbooks and non-fiction).

I just can't find the strength to read through any narratives, as all the busy work ruined reading for me. My least favorite portion of reading for school was being made to fill out entire tables of characters, with details on the mannerisms, presentations, quotes, etc. of each. It was all bullshit.