They do benefit immensely, but no by having "others fix and build" their own repos. You're overestimating the source code contributions and underestimating the cost to manage a hugely popular project.
> The Gameplan is to gain from the community, not contribute.
This is just silly. The """gameplan""" is to contribute and AND grow a community, which benefits everyone. Does it benefit more the company than the community as a whole? Maybe, but that's petty reasoning.
Even many companies who do eventually release parts of their secret sauce (e.g. Google, Facebook) first secure their financial and tech positions before they do so. In other words, when they do release their secret sauce, the good will they get far outweighs the risk of a competitor improving on top of their secret sauce and getting a significant chunk of their market.
Which is completely understandable? I can't see how things would be different and I'm still pretty satisfied with the outcome of releasing "the secret sauce" after it is a bit more stable instead of going through a turbulent development (looking at you, Angular).