Open source works best when it is a community. While there are millions of little projects that are buy one person alone, all the big ones (Linux, BSD, LibreOffice, GIMP, KDE, Gnome, GNU tools, GCC, LLVM, Inkscape, EMACS, Vi... the list is huge) are the result of many people collaborating.
The old "just work on your own" trope is simply a way to exclude people from a community. It's offering an alternative to being part of the community, rather than addressing the reasons why the community is difficult to join. Imagine if someone suggested that black people could just go and live somewhere else, they don't have to live in this particular suburb that happens to be full of white people. Don't create problems or animosity, just live and work somewhere else.