I tried that too, but sometimes the nesting level is too deep for YAML. There were also some difficulties when escaping special characters in YAML.
As for escaping special characters: I've run into that a lot, and I agree it is very annoying. God help you if you want to specify regexes on lines.
So for a lot of my YAML-ish applications, where YAML is used for user templating or configuration, I run everything through a really simple postprocessor (often by encapsulating non-digit lines with single quotes, and a few other tweaks) and that seems to work well for me. That way the user only has to type the bare minimum (no double quotes, no curly braces, no/fewer commas), and what they write "just works."