You say it all too well. Its a lesson, something many do well to learn. So long as you only write and about subjects outside your passions, the emotional investment on perceived rewards, after the long hours, is very high, disappointment, and thoughts of quitting are certain.
But like you in your experience, and not only you, me, included, by the way, and many out there, the experience becomes more interesting and less stressful once we climb down those high hopes and focus on daily events,people, life and paces, on our passions.
I mean, i write about my travels, because i love to travel. No stress. it all comes out easy. I spend little hours. Rewarded or not, i keep the satisfaction that i told of it, simple.
Thanks for affirming my thoughts, @filnette