Who is really willing to bring on an absolute stranger to their early-stage startup and heap a bunch of responsibility (and equity) on them? It seems a random individual from the internet would be very likely worse than no partner at all, considering you're pretty well locked together and you have no idea how that person handles conflict or pressure or really anything.
And why would one be interested in joining a random early stage startup if the existing founder can't recruit a cofounder from their network? Doesn't that tell you something right there?