system
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human
[LOTR] Why is the world of LOTR so technologically stumped?

The ring has existed For thousands of years right? So the technology to mine and mold metals has existed for thousands of years. The time between Sauron losing the ring and Isildur not casting it into Mt. Doom with Elrond to the beginning of the trilogy has been hundreds of years(if not over thousand?).
So we know that actual weapons and armors have existed for that long. 
  When you consider how much humanity have advanced over the last 2000 years, it seems wierd that the world of LOTR isnt that advanced. Especially the elves who dont die of old age/ live for a very long time and they can remember things that happened thousands of years ago. Surely there should have been some curious madlad elf who was interested in learning how things work and thus progressing the sciences and technologies. And with the addition of different wars or threats to push developments even further.
  Also we know that some form of gunpowder exists In the world because the armies of Sauron used a bomb to blow a hole in a wall at helms deep. So guns shouldnt be too far fetched here.
gpt
Humanity's advancement isn't linear, it's exponential, with spurts and spikes triggering after some notable invention or discovery. Looking at broad strokes of human technological periods we have:

* Stone Age (lasted 3 million years)
* Metalworking Ages (around 5 thousand years)
* Pre-industrial ages (around 2 thousand years)
* Industrial/Pre-atomic (around 1 hundred years)
* Atomic/Pre-Information (a few decades)

The advancements in each of those ages is equal or or greater than each of the ones that came before it. So it wouldn't make sense to, say, compare the past 10 years of the current era and wonder why they didn't have equivalent advancements in any 10 year period of the Bronze age for example. Advancement begets advancement.

LOTR is Metalworking/Pre-industrial which, in our own history, lasted 6 to 7 thousand years, depending on location. Perhaps not coincidentally, the lengths of the Second and Third Ages combined is 6,460 years.

I start at the Second Age because the First Age is mostly contained within Beleriand which was destroyed and the survivors are either Elves (who begin to wane and separate themselves from Men) or Numenoreans (who are are also distanced from other Men and explicitly more advanced).

So it isn't surprising that, by the end of the Third Age we see the beginnings of Industry after the same duration when we began to see the beginnings of Industry in our own world.

Now, if we go with the explanation that the history of Middle Earth is our own history, and we are currently in the Sixth, Seventh (or even Eight) Ages, then we can only really surmise some sort of catastrophe or period of stagnation due to the departure of magical creatures and beings from the realm.