My daughter regularly grumbles about her math homework. It's not that she usually finds it difficult, but that she resents having to do it at all. When it's easy for her she resents it more, because she sees her time as being wasted. Luckily for me, she usually does her math homework at her after school care (where all of the kids are expected to do homework at the same time), so I don't have to listen to the complaints.
Imagine my surprise the other morning when she asked to cut short our breakfast reading session so that we could work together on "math facts". She pulled out the workbook from a previous math module (they get to keep them after the module is completed) and started filling in unused pages. The next morning she asked to do the same thing.
So, when it's homework, she is annoyed and irritable about having to do it. But when it's her choice, she will happily pull out the same workbook and do the same activities.
It is possible that some of this difference stems from the fact that I'm sitting snuggled with her on the couch doing this "math facts" activity, vs. her sitting at Kids Club or at our kitchen table on her own. I could test this theory by doing her math homework with her on the couch (though this runs counter to my goal for her to learn to do her homework independently).
But I think it mainly boils down to free choice. When we're playing "math facts" she picks which pages look interesting. She stops to sketch on the unused backs of pages. She stops mid-activity if something is boring. When it comes to homework, it's not doing math that's the problem. It's doing a particular set of math problems that someone else expects her to do at a certain time, regardless of her own mood and inclination. The parallels to required reading are obvious here.
This makes me wonder: if her teacher were to assign her to read graphic novels every day as homework, would she grumble and complain and stop enjoying them? This is an experiment that I do not wish to undertake. Because it is quite possible that the answer would be yes.
It's all about free choice. Which is not to say that teachers don't have to follow a logical curriculum, or that my daughter won't have to learn that sometimes you have to do things on other people's timeline. But it's also true that self-directed inquiry is more engaging for her than assigned work, particularly in that outside of school time that she considers her own. This is probably the case for most of us.