That is the (build) circular dependency. OK if you are happy "downloading jars", but not if you are packaging for Debian: check the dates on this discussion https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=639910

Gnu make does not need make to build (it includes a build shell script for that), gcc can be built using any C compiler via a 3-stage bootstrap. But sbt, it seems, can only be built by sbt.