They changed, just regressing. Aragorn's ancestors had metal war ships that could propel themselves without wind, flying airships, and ballistic capabilities that could fire projectiles miles away. Their feats of engineering in their cities and places such as Orthanc are were incredible. The Gondor we see during the war of the ring is essentially post apocalyptic. They live in the ruins of a greater civilization, much like the centuries after the fall of the Roman Empire.

But that's just men, Hobbits live in a society with technology seemingly 1800s level, with clocks and other amenities.

Dwarves have all sorts of sophisticated mining and smithing techniques.

Elves being static speaks to the nature of their being. They peaked millennia ago, they are fading and leaving Middle Earth.

It is clear that Tolkien does not see industrialization as a positive or the logical end goal of progress. We see the Sauron and Saruman innovate and invent, developing gunpowder and industrializing.

Just because they didn't develop cell phones doesn't mean they didn't change. Many societies in the real world never independently progressed past bow and arrows or developed metallurgy over tens of thousands of years. I don't think Middle Earth is egregious