The main reason was because I discovered the power of templating. With Yadm it required an external dependency, envptl, then j2cli, and both of these became unmaintained, while chezmoi used the text/template standard library. After the task of converting my jinja2 templates to gotmpl I never looked back.
One of the other things I like about chezmoi is I significantly cut down any "scripts" to just a few as most of the logic became "deterministic", ie I would set conditions based on the host in chezmoi.toml.tmpl and then that would define how everything under that would run across multiple hosts, and devices.
If you make your dotfiles repo publicly accessible, you will leak your private keys unless you use other features in chezmoi to protect them.