Why we still use Makefile?

I think much pre-processing in the Makefile can be done with "build.rs", why don't we use most of the current Cargo tool instead of using the ancient Make toolchain? Maybe this is a stupid question, but which step forces us to use "make" instead of any other modern build system? I wish we can reduce the size of Makefile and use as much as possible with "build.rs" in the v2.0 if we can't eliminate the Makefile.

Start by reading the current Makefile and any build.rs files, then trace which preprocessing steps depend on Make. Document the steps that require Make rather than Cargo, and define completion as moving appropriate work to build.rs while reducing or eliminating the Makefile for v2.0.

Written by the indexing model from the issue text.