there are lots of embedded systems that run with glibc or musl shared libraries, if rust is used there, it will blow up the storage space with just a few executables due to the static stdlibs.
If you don’t have the budget for the standard library, don’t use it. If you somehow have the budget for glibc and not the rust standard library, call into glibc instead of the rust standard library.
rust stdlib will be bundled with those 20 rust executables, they blow up quickly.
mcu does not use stdlib of rust, it uses no-std, c++ has its own nonstdlib as well, on mcu they're similar.