You mention a number of things that don't really matter all that much, and neglect to mention the one thing that matters above all else:
A third-party, stand-alone tool doesn't have to work within the game itself without breaking it. That's why the good ones tend to be both better, and more flexible.
mmm, not saying that couldn't be a factor but, really, the single most important thing? more than "passion, no requirement to keep everyone happy, no managers, etc??". you really sound like a manager ...
but as much as a factor in favor it could be against. you know how it is like to deal with api changes that go unannounced and undocumented? to constantly reverse engineer some spaghetti api interface? to try and figure out what the last update screwed up? i'd say there is a reason some of these tools have had a hard time finding maintainers in the long run. even if it's a creative and inspiring project, dealing with crumbling or mutating specs is fun for just so long.
all of them have in common that they stem from works of passion, done by people with the knowledge and a clear idea of what to do, just plain and simple doing it, on their own.
that is the most important part in any project: intrinsic motivation. at a personal level it's energy utilization at its fullest potential. the moment you try to organize this into a business you start bleeding energy because different motivations start naturally competing. this is where "more is less". if you have exceptional management you can keep that at a minimum, but it's still a fixed cost. and the more energy your management sucks up the higher the risk you actually bleed dry and fail to deliver the project.
for some it's sheer passion for the game, for others plain altruism, for yet others an option to make something useful piggybacking on someone else's work and audience, to make themselves known or even, why not, make some coin with it. some may commit 2h a week, some 4h a day, but all that energy will really be used in focus, and that difference shows, it's usually work showing great love in the making (usability standards may sometimes suffer otoh, and you might disagree with some decisions but ... it's free, personal effort!
)
also, 3rd party tools are actually 'better' because they only compete among themselves, they tend to have no competition with the game because they are already granted that niche. game producers/designers have long learned they can depend on the community taking that up and that's a double win for them. not only don't they have to worry about that development at all, it also increases the perceived value of the product and its community. they would be dumb trying to compete and not profiting, even if they might sometimes appear 'outsmarted' to the occasional layman ...
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