Just curious what makes "The Cave" to be allergic to "Damage Indicator" mod?

That's actually intentional.

My goal is to turn The Cave into a single, self-contained package, so players don't have to keep downloading and managing lots of separate mods.

I integrated the functionality directly into The Cave, adapted and simplified the code to fit my own project, and gave full credit to the original author in the mod credits.

This approach also makes development and debugging much easier. Since everything is part of the same codebase, I can quickly identify where a bug comes from and fix it myself. I don't have to wonder whether the issue is in my mod or in someone else's mod, or wait for another author to update their code before I can resolve a problem.

My goal is to keep the code as simple as possible, minimize bugs and compatibility issues, and make maintenance much easier in the long run.

Your explanation doesn't explain why mark it as incompatible though.
I mean, you can just simply remove it from optional dependencies.

Yeah, if I had only bundled the original mod, I could have done that.

The problem is that I integrated and modified parts of its code directly inside The Cave. Because of those changes, loading the standalone Damage Indicator alongside The Cave causes conflicts and can crash the game.

If you're curious, feel free to try it yourself. Download both mods and run them together—you'll see exactly why I marked them as incompatible. 🙂