There’s a lot of foot guns in YAML. The specification is way more complicated with hidden obscurities. JSON specification is just 5 diagrams. YAML speciation on the other hand is an 86 page pdf, so there’s more room for nasty surprises (which is not a thing you want in configuration files).
I’ve also seen many people struggle more than they need to with the yaml indentation.
I think the only upside to yaml is that it allows for comments, but other than that JSON all the way.