You seem to be basing that question on the assumption that both options offer the same pay (or at least that both off "enough" pay). Working on your own project is a tremendous risk; and for every success story like this, my assumption is that there's at least dozens who fail or don't even make enough to pay their bills.

Working on a successful independent software project is, for a lot of people, much more desirable than working at someone else's company; in much the same way owning a startup company would be. But the key there is "successful", which is certainly not guaranteed.