- As yet another step on the way to becoming a career pilot, usually just before doing their commercial rating then becoming a CFI.
- As a way to be able to fly when the weather's not nicely VMC -- an instrument rating greatly increases the scope for flying, especially in a place like Coastal Northern California, with its coastal stratus.
- As a way to improve their flying skills and safety levels in general.
But the real reason -- as with learning to fly in the first place, and starting aerobatics training -- is simply curiosity. What's it take to get an instrument rating? What's it like? Can I do it? Etc. I'm more motivated by pure curiosity than most people seem to realise.