I’ve watched thousands of films and videos of air launched and air dropped planes and manned rockets, many of them shot during the fifties and sixties.
Personally I think it has more to do with how large the payloads we were trying to put up for so long.
We also really couldn’t feasibly produce a controllable mother ship like this till we came up with modern computer assisted flight controls and servos replacing hydraulics and cables.
Again … you are in my wheelhouse. Dealing with weight of the fuselages, the engines and the payload (the rocket) is a simple structural design issue. The dynamic forces generated by the two fuselages moving through turbulence is an entire different and highly complex issue. Each fuselage will pitch and yaw independently from the other, which will induce tremendous torque and shear stresses on the wing beam. Those movements, and thus the forces, would be lessened if the fuselages were connected at the tail, but presumably that would potentially interfere with the deployment of the rocket, so the plane was not designed that way.
Go screw yourself. In the box down below the thread I was typing in (suggested topics) it was at the top of the list showing 2 new posts I hadn’t responded to.