When he wrote The Hobbit, he was very much writing a fairy tale. So there was very little consideration for things economics and agriculture because it wasn't that type of story, and those types of things aren't important in fairy tales. And when he started to write the early drafts of The Lord of the Rings, he was still very much in that mode - it was intended to be a direct sequel to The Hobbit and the opening chapters have that much more light hearted feel to them.
But the story grew in the telling, and by the time he reached the end of of The Lord of the Rings he was far more invested in realism and consistency within the world - so was paying a lot more attention to this type of thing (including going back and editing and rewriting sections multiple times).
This is also very evident in his other writings. The first drafts of what would become The Silmarillion were very much more fantastical and mythic - we got stories of a flat world and very brief and vague descriptions of the Elves awaking under the stars before the Sun and Moon were made, and marching across the land. The versions of that same story he wrote towards the end of his life had a round world, and carefully planning out of the Elvish aging and reproductive cycles throughout the march, to work out how many generations would be needed for there to be a suitably large host.