system
Given the following post, respond as if you're commenting on Reddit:
human
[LOTR] Did the Elves suppress Men's innovation in the Third Age?

Its often asked why in the Third Age Men never get past medieval technology but it's also well known that the Elves want to preserve the world as it is. Could it be that the Elves selfishly advised Men into behavior that doesn't favor innovation and once the Elves left in the Fourth Age, Men were free to be inventive?
gpt
No, that would require waaaaay too much interaction with Men than the Elves left in Middle Earth by that point wanted to have. 

The Third Age was very much a Dark Age in general for the world of Men. Consider that the only major kingdoms anywhere near Erebor to begin with were refugee states founded by the handful of Numenoreans to escape the wrath of the Valar, and in addition to the depredations and destruction caused by Sauron directly and his minions (chiefly Angmar), as well as the wars fought against easterlings and southrons, a huge plague swept through Arnor and Gondor and their surroundings only a century or so before the events of LOTR. The whole back half of the Third Age was about the Realms of Men getting the ever-loving shit kicked out of them, while Elves continued to turn inward and retreat from the world. 

There's not going to be much innovation at all going on in such a world. 

Now, after the final defeat of Sauron and the creation of the Reunited Kingdom, you've finally got a growing population and the political stability needed for some good, solid technological and sociological progress.