How did you get that from what I said? JSON isn't included in Rust binaries because of its ability to bring in only what's needed, and my ability as a developer to specify that as a fine-gained level at compilation time.
Using a language where you don't bring things in as needed means they're built-in at the interpreter level or some other scheme like a large required standard library.
Maybe in those languages your compiler is smart enough to filter out unused code, maybe you don't even have a compiler and you have to distribute your code with an interpreter or a virtual machine with all the batteries. Either way, languages where libs are brought in as-needed are at an advantage when it comes to compiler tech to generate such binaries.
Using a language where you don't bring things in as needed means they're built-in at the interpreter level or some other scheme like a large required standard library.
Maybe in those languages your compiler is smart enough to filter out unused code, maybe you don't even have a compiler and you have to distribute your code with an interpreter or a virtual machine with all the batteries. Either way, languages where libs are brought in as-needed are at an advantage when it comes to compiler tech to generate such binaries.