Maybe not always, but surely in most cases of too complex a config, it is a case of ad-hoc grown config, representing what one wants to actually configure badly, and/or underlying abstractions of the thing one wants to configure matching badly what one wants to do. In most cases it would be good to take a step back, or multiple ones at that, and really ask oneself: "What is it, that I actually want to configure here?" and think about why it cannot be a simpler config. What abstractions would actually make expressing that config easy.
Often one will get to a very simple config format in the end. Of course, when one has to deal with very complex formats created by others, already widespread in use, on cannot easily change the format. Maybe that is the reason we get these meta config tools.
Sure. There are undoubtedly a lot of config formats that are overly complex.
But sometimes the complexity is irreducible. Kubernetes is one such case. The model is very well thought out, and just about as simple as it could get without removing functionality. It has sensible defaults, built-in versioning, well-defined schema etc. But if you want to describe a complete installation of a distributed system with many heterogenous processes, spread across many hosts, communicating in specific ways, with specific permissions, persistence, isolation, automatic scaling, resilience, etc, there are a lot of details. I've worked with systems that have thousands of lines of configuration, and honestly that's not extraordinary. Many people on this site will rightly scoff and say, "psshh, that's nothing."
Configuration languages are a really important area of research in the tech industry right now, and every time someone posts one on here, there are a huge number of dismissive comments. Fine. Not everyone has this problem, but it's a real problem, and solving it represents a real advance in the state of the art.
Often one will get to a very simple config format in the end. Of course, when one has to deal with very complex formats created by others, already widespread in use, on cannot easily change the format. Maybe that is the reason we get these meta config tools.