Starlark is a language that defines how software is built, and as such it is both a programming and a configuration language.
You will use Starlark to write BUILD files, macros, and build rules. Macros and rules are essentially meta-languages - they define how BUILD files are written. BUILD files are intended to be simple and repetitive.
All software is read more often than it is written. This is especially true for Starlark, as engineers read BUILD files to understand dependencies of their targets and details of their builds.This reading will often happen in passing, in a hurry, or in parallel to accomplishing some other task. Consequently, simplicity and readability are very important so that users can parse and comprehend BUILD files quickly.
When a user opens a BUILD file, they quickly want to know the list of targets in the file; or review the list of sources of that C++ library; or remove a dependency from that Java binary. Each time you add a layer of abstraction, you make it harder for a user to do these tasks.
BUILD files are also analyzed and updated by many different tools. Tools may not be able to edit your BUILD file if it uses abstractions. Keeping your BUILD files simple will allow you to get better tooling. As a code base grows, it becomes more and more frequent to do changes across many BUILD files in order to update a library or do a cleanup.
Do not create a macro just to avoid some amount of repetition in BUILD files. The DRY principle doesn't really apply here. The goal is not to make the file shorter; the goal is to make your files easy to process, both by humans and tools.