Underscores vs dashes in crate names?

I notice that many popular crates use dashes in their crate names. Is there a rationale for this?

My first thought would have been that underscores would be preferable (to match the use of the crate in source code, since code allows underscores only), and I tend to use underscores in my crate names.

But it seems like big / high-quality crates more often use dashes, and I'm neurotic enough to feel like I'm marking my work as "more-likely-to-be-clueless" by using underscores.

So: Is there a technical reason to prefer dashes?