I would estimate that I did about 25% of all reading assigned to me in high school and undergraduate (by volume of pages, not assignments). I wish I could have read just about every page of it, but I did not have the time or mental capacity to.
For me, reading (a textbook) was the most mentally strenuous homework because it requires me to maintain a high level of focus the entire time I am doing it and taking a break (outside of designated chapter/section boundaries) risks losing context. Solving a set of problems is much easier. The first problem is hard because I need to look back at my notes and skim the text book to remember what problem solving approaches I am being taught. But if after solving that first problem I see that I am out of time or energy, I can easily put down the assignment and come back to it later. For the next several problems, I could simply look at how I solved the first and be 75% of the way towards solving the rest.
It does not help that professors would be selective in how many and which problems they would assign as part of homework (since they would have to grade it), but they would assign chapters to read without considering the total volume. Even worse, the most effective way to stay engaged with reading is to take careful notes, so reading would take 3 times longer.
Despite that, I have always enjoyed reading for pleasure, though I have not always been able to find the time for it.