The article recalls people that open-source software is not necessary created for the community, but rather by the author, for the author oftentimes.
The "support" is not only the maintenance burden which (sometimes) could be solved for money. It's also the features that the original author just don't find useful at all, but others may want to have.
If I don't have Mac, never used it and don't plan to buy it, why would I want to accept contribution to support this platform? It's useless for me, I won't be able to test it (and it will break sooner or later), and once the code is accepted, it's usually assumed that it would be maintained by the application author, not the code contributor (unless additional CLA is signed, etc).