About, maybe, two years before I started writing on HubPages, I had just started doing some offline freelance writing again after not having done it since my children were young. When I discovered "writing sites", it seemed like a good way to get practice (again) at "writing on demand" (writing what I could come up with after seeing a title suggested). I did that for awhile and found I enjoyed "just writing what I wanted to write" (but on another site). Once I was through feeling like I could use some "writing-on-demand" practice, I got a bad "flu thing" that left me exhausted for about two months. Since I at least had the energy to write, I went to that site and wrote up a storm whenever I had some free time but still not enough energy to do much of anything else. That site changed and started wanting to people to write "web articles" (as opposed to "whatever they wanted"), and that's when I searched and found HubPages.
As a freelance writer, a person often has to write what someone else wants him to write. A writer who works full-time for a company always has to write what someone else wants him to write. When I started writing, I'd never really had the time or chance to just write what I wanted to write; so the idea of doing that was appealing to me. Although I wanted/needed more money at the time, I didn't believe anyone could earn by writing on a site like this. So, my main motivation was to just enjoy writing, but also, maybe, share some of the stuff I think I've learned over a few decades of living life (and particularly since I've had some experiences a lot of people either haven't had yet, or else will never have). Once I began earning some extra money on here I just kept writing. My freelance business isn't all that "booming"; so, the more income, the better.
It's always seemed to me like using my spare or skimmed time to do what I enjoy on here (or a few other places) is a productive, but also pleasant, use of free time. With the Internet's becoming less and less a "just write what you want" place, my offline working picking up, and my kind of having lost sight of "what I want to write" anyway; I'm now in the process of re-thinking my approach/aims and getting a little more back in touch with my "writing roots" (which is one of the nice things about writing online, or offline). :)
All that aside, I have "a thing" that people don't understand one another very well. Sometimes that factors into what/why I write. :)