Along with performance, there's probably other ABI issues and maybe even API extensions to the C library that just aren't present in these tiny implementations.

Along with performance, there's probably other ABI issues and maybe even API extensions to the C library that just aren't present in these tiny implementations. You can work around the ABI stuff by recompiling with the new c library of course, but that won't work if you've got a closed source binary or if the software needs something not provided.