I can see why that is much more appealing, the coop is so low to the ground and has so little height to it that there's no way to make a roost inside more appealing than the one outside. If the run is predator proof, I don't see any reason not to let them sleep outside vs cramming into a small...
Since the ramp removal was what caused this, have you tried simply putting it back?
Nest boxes are for laying in, chickens should be roosting at night unless there's a reason for it (i.e. Silkies may not roost).