I suspect that it's the "just", for reasons that sibling commenters have discussed. But the original comment might also wrongly come from the perspective that

I suspect that it's the "just", for reasons that sibling commenters have discussed. But the original comment might also wrongly come from the perspective that a given developer ought to tie themselves to a particular project by creating a business around it. Many projects are created and/or maintained by developers working on a broad number of projects, so total productivity might decrease if developers were settle down with only one or two projects which they're able to build a business around.