Here's the thing. We've basically been using TOML since the INI file format from MS-DOS. It works, and it's useable, and we've all seen it. TOML is just an evolution of the INI format to fix some of its shortcomings. YAML blasts onto the scene like "hey, what if we just rewrite the JSON format to make it legible?" which brings with it a million edge cases of problems.

YAML is the new kid on the block. And despite having several great formats for different use cases already, some kind of mass hysteria caused big players to adopt YAML. I suspect everyone who adopted YAML is either a Python dev or they were drawn in by the legibility of the format. It's easy to read. While that's true, did anyone stop to think about what it's like to actually use the format?