I think that for most honest people it's a combination of both. You can post about something that you're truly passionate about, but at the end of the day, you'd also want to earn something with it.
Personally, I like posting about stuff from my day to day life, it doesn't earn that much, but it's fun to do so. On the other hand, I'll also post stuff that I think might do a bit better than the usual day-to-day stuff, because it's fun to see your work being appreciated.
Full disclosure: I use Minnowbooster on some of my posts and usually I only use it once for less than 1$.
There is nothing wrong with promoting your content if you are into that, people do that on google facebook, etc. Point is wrong content gets promoted more and for wrong reasons.
Admittance is good.