With babies I think it's just learning how things work. Ramps can be a huge learning curve for some of them.
With adults, well I think it's personality. All but 2 of mine always go back to the coop before dark. My 2 polish, who we call the Derps, will either try and roost in my rhododendron which is right in front of my bedroom window and then smash their faces against my window to sleep. I have to go out and scoop em up and put in the coop when I go out to shut things down. If they can get into the mud room, they head for the dog crate and try and roost on my poor 19 year old aussie, maybe lay an egg on him while they are at it. (he doesn't mind that though, and will happily gobble up the egg) Sadly one of them is getting rather arthritic so she is going back to the coop more often now instead of trying to jump in the bush. Who knew I'd be sad to not see her face smashed up against my bedroom window at night.
Your coop design is really cute and it looks like you really did your research and planned well for it.