Why “Lord of the Rings” feels real and “Narnia” doesn’t

Narnia doesn't feel real to me in the same way LOTR does because our world is involved in it. All isekais are like that to me

They are both well written, and when I'm in the middle of either book I'm completely absorbed in its world. In that moment, I'm not thinking about realism at all.

It's only when I put the book down that questions like that come up.

Interesting? Less than six minutes long? No ads? I’m astonished!

This is just a freestyle thought, but I think it may be in part to where the fantasy elements are drawn. For example, things like elves and hobbits are humanoids, portraying mainly humanoid traits -- just exaggerated like living a thousand years or having short height with massive feet. Or things that are purely imagination like dragons. Narnia, on the other hand, seems to make real life things betray what we know about them; like a talking lion. We have lions in reality and they don't talk. We don't have hobbits and dragons and elves in reality so we don;t have hard, preconceived notions about how these species should behave like we do with lions which makes us tend toward "realistic but alternate reality" vs "fantasy". This is just a rudimentary thought though.