Being honestly, I guess I've never asked through my whole life that question before... I would rather go with "St. Augustin" and confess that I can't remember. But it's indeed sweet to theorize it: I don't feel that I thought to "need" to learn Portuguese in order to achieve anything, this materialistic approach doesn't seem me plausible, so it was perhaps for curiosity? A sort of natural and immediate response to stimulus? Something I brought from a past-life and learning it was like the remembrace of Plato's Republic that I would have much time later?
I would raise a different question: when you first fell that your effort to learn portuguese definitely worth the effort?
The curious is that I can't answer that either, once I don't remember for sure how much effort it actually took.