Your comment made me wonder if crates.io is starting to show some of the same issues that npm has. Lots of small packages, not always consistent, focussed on one use case that make other use cases non-optimal.
The recent posts about Rust in Android shows a side of this. They are avoiding Cargo in favor of plugging in their own build system. Use the language for its benefits and avoid the ecosystem (partly).
I think the case with embedded code on crates.io is more along the opposite: they're trying to make the experience as consistent as possible by defining common interfaces for embedded drivers so code can run consistently with different hardware or libraries. The problem is it's really hard to design such abstractions, especially safely, when you can't make many assumptions about the hardware it'll be abstracting over and efficiency is paramount.
The recent posts about Rust in Android shows a side of this. They are avoiding Cargo in favor of plugging in their own build system. Use the language for its benefits and avoid the ecosystem (partly).