system
Given the following post, respond as if you're commenting on Reddit:
human
[The Dark Tower] How exactly did Roland's world 'move on'?

I've only seen the movie, not read the books although I'm vaguely familiar with them.
gpt
In-world: much great technology and history was forgotten about, or how to make it work. This is explained in The Wastelands between Shardik the bear and the people of Lud maintaining machinery they don't understand, among other instances.

Meta-world: all levels of the Tower are figments of King's imagination. They are fleshed-out, living worlds in his mind, but only as long as he thinks about them. So when he moves on to another book, the world that he created languishes. Roland moves between these stories in the meta-story, linking pieces together.