Also seeing as cliff is wounded in the beginning, it appears to me he may have developed that baby tech, and then died somehow, got .. and now is on some weird mission in hades, like some mercinary, having dolls as a representation of babies, like he is without clear memory, but still has these strands.. of his persona.
So my theory on Cliff is that he became obsessed with finding a solution to keep people linked to the real world. (death stranding causing craters when you die and if you dont have a connection to the real world you get lost in hades, and get absorbed by it) so he developed the Bridge Babies (BB's). Bridge babies being his.. well baby project! (damn you kojima for naming things so literally, makes it hard to explain.) So at some point he died, (the trailer opens with him singing to the BB with blood on his face, slowly dying) and got lost into hades, he died before his project was complete so he has no real connection to come back. It also explains the dolls, they are like representations of the BB's to him. maybe he is trying to communicate (Dead men tell no tales). and he literally haunts you in the afterlife, his soul corrupted by the underworld.