So does a Makefile.

A makefile works great when you have a pile of source files and you want to make a parallel pile of output files, and each source file is compiled individually. It's not so great when you have a compilation process where you have a folder of entrypoint source files that each need their own output artifacts produced but they happen to share many dependencies, and you want to automatically create common output chunks if there's enough overlap between them, etc. I'm sure you could find a way to involve Make by automatically generating makefiles, but at that point, Make is only handling the really easy part and isn't worth it.

Think of how many makefiles just end with one big linker call. Most web toolchains (which crunch a lot of source files into a few artifacts) have more in common with that linker call than the rest of the stuff that happens in a makefile. You have to have a system that's more integrated with what's being built to make that step meaningfully incremental.