LoTR had an industrial revolution. It was called Isengard and people didn’t like how it turned out. Elves were anti technology so there would be downward pressure until they upped and left. Dwarves probably reproduced slowly and were recovering from being orc and dragon chow. Numenorians reproduced slowly and they were also recovering from the plagues and wars. This leaves hobbits who were idyllic. Oh, and the wizards were forbidden to show their abilities.

When the age of men begins, the modern world begins. Tolkien was not interested in writing about that having seen it’s horrors first hand. And as others have written, the population density was very low. Rohan mustered 7-10k riders from the adult male (+1j population.