He warned us long ago that
Anyone inheriting the fantastic device of human language can say the green sun. Many can then imagine or picture it. But that is not enough—though it may already be a more potent thing than many a “thumbnail sketch” or “transcript of life” that receives literary praise.
To make a Secondary World inside which the green sun will be credible, commanding Secondary Belief, will probably require labour and thought, and will certainly demand a special skill, a kind of elvish craft.
But I think that his influence on world-building has discourage people from saying "the green sun" which is a necessary precusor. Sure, you can work out the exports of your country -- wheat or porcelain or silk -- but how drab is that? We could always read about exports in an encyclopedia. And it's always a temptation to not say "the green sun" -- or to say, and then forget it. Ambling along, describing incidents and settings, it's always easy to reach for the familiar and forget that the green sun will make things different. World-building won't always help with that; it may, by its pressure to make the world plausible, harm.
And, on top of that, it also precludes a lot of wild, wonderful, whimsical worlds. Animated playing cards or chesspieces as characters? Kingdoms of personified words or numbers? Faerie with a tendency to wander farther or nearer to mortal lands? If you try to build a solid world out of that, they will laugh at you and run away, and you will not catch them. If you, drawing on folk tradition, tried to make a land of food where it snows popcorn and the rivers are lemonade, and the houses are build of gingerbread -- could be great fun, but trying to world-build with it would drive you crazy.