Do you need a "calling" (for want of a better word)?

I've been singing for a while, mainly traditional, mainly unaccompanied. During the past year or so, I've been caught off guard by people asking me, "So when you going to write your own stuff then?" It had never occurred to me before - I thought that it would be something you did because you couldn't not do it (am I making any sense here?)

Of course, now that the idea has entered my head, it's left me with a wondering itch...