

It’s important to distinguish between interaction and constraints. Electromagnetic radiation is a connection, in a sense, but it is not functioning as a constrain, I. E. it does not mechanically link the two bodies. While they do have an effect on each other, their interaction with spacetime is still separated.
Hubble flow is only disrupted if two bodies in a system have a spatial constraint. Radiation does not provide such a constraint. Gravity can, under some circumstances, but it is not considered a rigid constraint in most cases.
General relativity is weird, I know.





Do you want to piss off a balrog? Because that’s how you piss off a balrog.
That’s why he fought Gandalf: Magic breaks physics.