The real point of make is it's a declarative build system. You just tell it to make and it will do what needs to be done by figuring out dependencies and rebuilds.
A Makefile with tasks that just run external scripts is much easier to find than the scripts directly. Add some help texts and it’s a great DevEx multiplier.
With a Makefile I can generally just run `make` or `make <tab>` to have a feel for what's available. It's right there on my terminal, which is usually the first thing I interact with when I open a repository. If enough of the engineers use it, it stays up-to-date as it gets fixed and updated along with any other changes.
Documentation OTOH has a tendency to be forgotten and left for dead. IME this is especially true for internal documentation, and the closest to the code the docs are, the less attention they receive - since higher level documentation is more likely to be consumed by people outside of the team.
With a README, I need to:
* remember to read it * trust that it will have the information * trust that the information is up-to-date * finally, figure out paths to scripts, arguments and/or copy-paste commands