Much of mine happens "in the moment," as well. Originally, my intention was to get something done with the 100's of notes I have with scribbled ideas I never developed... but I have maybe gotten to about 10-15 of those; everything else has been "new."
"Popular," for me is coincidental/accidental... just depends on what I am posting. Writing about cryptos and Steemit tends to be well received and I did make quite a bit off a couple of posts... but that doesn't inspire me to make that my song of one note.
But we all have our own reasons for writing; for me, it's often an exercise in "clearing my head."