While everything you said is valid, sometimes that question is pure curiosity. "Because i want to" is completely valid, though I'd love to know what the inspiration for that desire was. Did you hear a really cool battle song? Some orchestral piece that sounded great? A friend recommended it? Couldn't find an ocarina? Jamming to some folk metal?
I swear I'm inquisitive!
That's fair, though I might possibly (albeit unlikely) respond that way, but the reaction would be more in surprise as opposed to disdain.
Perhaps I already played the flute and the individual jokingly gave me a hard time over it, now they're playing the flute? Why!? You're one of us now!