I discovered TOML a couple of years ago when I started playing with Hugo, as it was Hugo's format of choice for configuration files. I honestly find TOML harder to read and more complicated to use than YAML. I tried to look into it but frankly I still haven't found a use case where it made more sense to use TOML.
There's been times I wanted YAML support in a particular app; I've never wanted TOML support. If anything, it's been "ugh, I have to use TOML".