Just adding something quickly that I've noticed (as a student of course), the main thing that comes up is repitition, we do a lot of that but it's "hidden" IMO. For instance when we do modern self defence, we train the exact same things over and over and over and over each time. If the attacker does something different, we still train the exact same thing and that's because we train principles rather than set "You must respond with Option A to Attack A, Option B to Attack B" etc.. Given that there are so many possible scenarios etc and classes are so fast paced, it can seem like you're learning something brand new.
That being said, something I commented on in class a while ago while doing knife defence was that the material was very familiar, almost unchanged but I got so much more out of it after some extra time spent training and then being exposed to it again. Each time we revisit the basics I find I get something new out of it, whether that something is an understanding of a concept or as small as figuring out a tech works easier for me if I shift my weight this way instead of the other. That in itself keeps it "interesting and fun" without needing to go through something new every time, for me anyway.
Generally the practitioners in the JSA initially try to collect kata, you want to learn/know as many as possible as well as all the variations that go along with them. You train other schools, you question your sensei about things, and you build up in your head a list of all the kata you know.
After a while you start to realize that the way you move in this school, is the same way you move in that school, and this kata is really the same as that kata, with a bit of flashy bits thrown in. Then one day you realize .its all the same! At this point you start to strip it all down to the basics, and you just try to become proficient at what is the core of your school.
There are such so many ways to swing or avoid a sword.