Nothing. Even if it's objectively terrible (thousands of lines of templated YAML, or thousands of lines of spaghetti bash), being in Git as code is still better. At least you know what it is, how it evolved, and can start adding linting/tests.
I manage large IaC repos and it's mostly HCL, well-structured and easy to work with. Where we have Kubernetes manifests, they're usually split into smaller files and don't cause any trouble as normally we usually don't deploy manifests directly.
