For me, it depends on the money, the project, and my financial situation. With a stable salary currently, I often find attempts to make money from my side projects more demotivating than motivating. If it's something I actually find interesting, it's a hobby. Maybe it's writing software, maybe it's editing Wikipedia, maybe it's writing essays. That feels like a good use of my time, and I get to decide if it is or not. But then if I try to find a way to make money at it? Now it turns into basically a job, where I need to figure out how to monetize it, and in all likelihood the hourly rate will end up depressingly low. So I'd rather just spend my hobby time as I choose and not worry about monetizing it.
More subtly, I find that having monetization as a goal of a side project can creep in in a lot of ways that aren't really beneficial to the project. Take even just writing something. Sometimes I'm frustrated by the information available online on a subject, and want to spend a bit on writing something to set the record straight. Sometimes this makes sense to publish myself. Other times it makes sense to write or improve a Wikipedia article. This is an interesting tradeoff, because it's basically trading likely many more views (therefore likely more impact) if I write it on Wikipedia, versus more control and authorial credit if I post it myself. From a monetization perspective, writing on Wikipedia is rarely the optimal choice; but from the perspective of getting the information out there, it sometimes is.