Have they ever roosted on the roost?
The roost looks pretty close to the wall, so it may not be a comfortable distance for them. If their tails or heads are up against the wall they won't like it. Also, that jump is a lot. A ramp or something that steps up would be easier for them, even stacked hay bales. I try to keep jumps to 18" or less to minimize leg and foot injuries. They tend to jump down, and that's a long jump. I saw another roost a few months ago, similar situation, once they moved the roost farther from the wall they started using it. I think I would enlarge the lip on the nest boxes, wide enough for them to walk it, move the ramp to the other side, and make another ramp for your roost, or stack hay bales. I think I would lower the roost also, and make it farther from the wall.
Another observation, the spaces in boards in the wall are large enough for mice and snakes to get in, I would cover with hardware cloth. And that ledge is a perfect rodent run. I wouldn't be surprised if you start seeing mouse droppings along it. if there is feed, even undigested grains in the droppings, mice will come.