A build DSL solves the problem of making your build rules and systems first-class citizens. It's not just learning a new syntax—in fact, since you're embedding into a known language, it isn't even that new—it's about getting more control. You can pass rules around, modify them and do whatever arbitrarily complex tasks you need in a natural, straightforward way using your favorite programming language. You don't have to contort yourself and bend over backwards to fit the logic you want into Make's limited and peculiar language.

Your build system is an integral part of your whole program and you want to treat it just like any other code. This means refactoring, this means modularity, this means libraries, this means no copying and pasting... All this is far easier with a system embedded in your main language than in Make. You can use your existing tooling, debuggers and frameworks to support your build system. If you're using a typed language, you can use the types to both constrain and guide your build files, making everything safer.

Using an embedded DSL integrates far better with the rest of your ecosystem than relying on Make.

Apart from making the logic of your build system easier to describe and maintain, an embedded DSL also makes arbitrary meta-tasks easier. You might want to monitor random parts of your build process, report to different services, connect to different front-ends (an IRC bot, a CI system...) and maybe even intelligently plug into the features of your main language. Wouldn't it be great to have a make system that's deeply aware of how your server is configured, how your type system works, what your compile-time metaprogramming is doing an so on?

You could just glue together a bunch of disparate scripts with a Make file. Or you could use a DSL and call these services through well-defined, maybe even typed interfaces! No need for serializing and deserializing: you can keep everything inside your system.

Sure, if you're just going to use your DSL as a different syntax for Make, you're not gaining much. But it allows you to do far more in a far better way, while fitting in more naturally with the rest of your code. I'm definitely all for it!