>>212362640
Cause he wanted to keep expanding Narnia as a setting. He was good friends with Tolkien, and like Tolkien he was engaged in world building, though he didn't go to the extreme lengths Tolkien did because he lacked Tolkien's background as a linguist, and Tolkien's more peculiar beliefs about the importance of language to mythology and identity. Both Tolkien and Lewis understood though how a place can be made real by telling stories about it. That is, essentially, the whole point of high fantasy. You make people believe in a place as if it were real through stories. Lewis was more focused on the stories showing different parts of Narnia, different eras, different people, to make it seem vast and ancient and lived in.
Tolkien also did write a great deal of stories set in Middle Earth, most of which were never published while he was alive, but they had different priorities for creating a world and what they were trying to accomplish with it.
