Ask HN: Finding open source collaborators (is the open source too fragmented)?

There is a vast number of open-source projects out there. Which is certainly very good. From my undestanding most devs want to make something of their own from scratch. We come up with a lot of ideas on the way and sometimes seems easier to do it yourself than participating in someone else's project. Also, "mine does A others does slightly A but also B and is much too complex" notions appear when you first may glance at a project. Of course all great things start small and prove their value through the community, one might argue, but wouldn't it be better sometimes to concentrate efforts on more "valuable" projects? What might be the channels of promoting (even advertising) open source projects and somehow rank their value?