I made an extension to my old small prefab coop when I had my first offspring.
This was light and airy and turned out as a much better roosting area for them.
The chickens and chicks moved in the extension themselves. And only went back to the small coop one day when I was still cleaning their coop at roosting time. The next day they roosted in the extension as usual again.
It’s true that most prefabs are small, have not enough ventilation , sometimes not even a window for natural light, roosts are often too low and they often have too many nest boxes. The roosts should be higher as the nesting boxes to please most chickens.
Another thing that might be a problem is social interaction. Pecking order can be harsh for some chickens. I had one pullet that started to sleep in a nestbox for that reason. Other hens bullied her when she wanted to roost. I tried to put her on the roost with the others for quite some time. And after this failure, on a roost in the old small coop. But she got company there too that bullied her. I finally gave up. It was not because she was stubborn, but because she feared the others and felt safer in the nest box.
It needed time to heal (mentally). One day she finally slept on a roost in the small coop a few weeks after I made second higher roost for her in the small coop. End of problems.
Last winter the flock dynamics changed because my oldest hen disappeared. And ever since (until I had two broodies) the whole flock roosts in the extension. She moved in there by herself.
Now one nestbox is taken by 2 mommy’s and 3 chicks.
If it was my coop I would add some space, light, hwc ventilation, another higher roost. The roost bars on the bottom are quit strange imo. Do you have these in you’re coop too?
A wooden coop is easy to adjust with some building materials.
Make a few pics of the coop inside when the chickens are in and ask for some clever advices.