I've had the similar experience, of working on personal projects quite close to undergrad coursework yet having a huge difference in my motivation between them. What helped me was the modules that really fit with levelling up my knowledge (for instance a report on System/360 microprogramming).

It's always seemed to me that this kind of person should be a good candidate for postgraduate degrees: driven in their own exploration, effort on interesting things, etc. I've never managed to really find out the reality though.