Because submodules absolutely suck, and if you have the option of merging the two repos, they're 1000x more terrible. This terribleness increases nearly linearly with the number of active project participants. Why? Because they completely violate Git's operating model, which is to track content, not pointers to content. This is the fundamental problem, regardless of project dynamics, Kubernetes, whatever. In fact, that they make "git commit", one of the most fundamental operations you can perform, significantly riskier, because you can easily introduce submodule pointer changes from your dirty working copy. And people do this all the time. One of the most common cases is committing a submodule "update" while accidentally in a dirty working tree, so when you push the commit pointer simply doesn't exist anywhere. They also fail immediately once you try to `git merge` (or less commonly, git cherry-pick), because their merge conflicts, by definition, cannot be resolved automatically. Because they are pointers, not content. But git works on content.

So just to be clear, two of the most fundamental day-to-day operations you can perform are turned into massive liabilities from this feature, ones that are likely to either break your build and/or just make your life harder. As someone who had to maintain stable and development branches of a project, cherry pick between the two, cut releases, etc, submodules are simply hell, because they make an already difficult job worse. This is a good sign that they are a liability. In a past life we actually had so many people push invalid submodule updates over time that we eventually wrote a git hook on our server to reject all commits with submodule updates that didn't exist in the corresponding repository, and that were not specifically tagged in the commit message as updating a submodule (through a magic set of keywords.) The fact we even had to do this is its own pain.

I have maintained projects that have long-standing histories with dozens of submodules. And every single time we eliminated one of those submodules (often by merging into the parent repository, or simply dropping the dependency entirely), we all breathed a sigh of relief, and our lives all got significantly better from that point forward.

As you can tell, this experience has made me very prepared to fight against submodules everywhere I might see or encounter them. But trust me: it's for your sake, not mine; 'cause there ain't a chance in hell anyone is adding any to my repositories.