I feel like Rust without std might as well be a different language. Almost all of the available mindshare, docs, libraries are dependant on it.
Sure, you can use it. But to me it just looks like technological poverty. Even compared to the C ecosystem.
There were sufficient crates to write a ssh server for a rp2040 (mostly out of curiosity) using what's available in no_std.
That repo has a few crates depending on each other - sunset is the toplevel ssh, sunset-embassy adds no_std async, then the async dir has std rust, with a commandline ssh client in the examples dir.
There's obviously a lot of need for improvement in Rust in regards to small systems, as people have pointed out. But there's also a lot more middle ground in Rust vs, say, C++: You can be no_std and still have Vector, for example, while in C++ the STL is an all-or-nothing thing.
It's a smaller community, and it will come down to individuals deciding it's important and making contributions.