Remember that a compiler generates an executable file (can almost be thought of as an ASM transpiler), this file must contain everything the language needs to operate (oversimplification) so that includes the runtime as well as the compiled instructions from the user's code. This is compared to an interpreter which doesn't require you to pack all the implementation details into a binary, so instead you can use the host language's runtime.

All this to say: the output of a compiler is by necessity not tied to the language the compiler is written in, instead it is tied to the machine the executable should run on. A compiler "merely" translates instructions from a high level language to a machine executable one. So stuff like a GC must be coded, compiled and then "injected" into the binary so the user's code can interact with it. In an interpreted language this isn't necessary, since the host language is already running and contains these tools which would otherwise have to be injected into the binary.