That's exactly it. If my own projects were paying the bills I'd be working on them full time. As they don't (yet!) I'll trade a bunch of my time for some guaranteed income working on something not as interesting.

That's not to say I'm only there for the cash - I legitimately do like my job - but the salary offered is the sole reason I started working there over anywhere else. Raises and bonuses are what'll keep my eyes from wandering over other job ads in the long term.