I think many people understand success as results. Developers release games and possibly get money selling them, which is seen as success. But you could think it another way, success as opposite of failure.
Some roguelike projects fail, because developers not only abandon the project but they sometimes completely end their game programming hobby or career and move on to other things in life. I guess it's ok, but it's an actual failure: you failed in whatever you tried to do. But if you just keep on going and don't give up you can't fail. You will always be successful as a creator, and that can't be measured by achievements or the amount of money you make.
There is something in the way people react to long term projects. They try to ridicule it, but I think secretly they wish they had the same kind of persistent willpower to never give up. In many cases people who do become successful in real life terms (money etc.) have that trait and for them life is all about trying to reach something, some kind of goal that's always around the next corner.
I guess I'm a bad case of that trait, because I never understood people who abandoned their game development life. Why would they do that? What made them stop?