Now, my world is old. Very old. And, unfortunately, the story locked me in a paradox. Namely, the colonization of the lush caves featured in another of my questions, which also have a name now (Harat Caverns). You see, a small group of intelligent dragons colonized this place 3.5 million years ago. They were in the renaissance age. How can I prevent them from progressing beyond the early industrial point? And, as a side note, why would they prefer medieval weaponry and customs? Do note that magic does exist.

Edit: Welp, apparently due to bad writing on my part, everyone thinks I'm just talking about the dragon civilization. I'm talking about the entire world. Also, if it helps, the setting is a large archipelago in a mostly temperate zone. I also still want the use of fossil fuels. And there are humans, as well as 8 other races. And the dragons. Sorry about the misunderstanding. Have upvotes as a compensation.

Edit 2: I had an idea. I decided to come up with a special deific monster called a Watcher, or numina. While they've been around for a while, I only just realized how I can apply them to this. You see, numina used to only stalk roads at night, killing travelers, but I realized that perhaps they can prohibit other things as well. Do with this as you will.