Scala's feature-space is admittedly crowded, but there is a method to the madness.

Scala's core design is generally to use a small number of rules to create a wide range of possibilities; the macro design they've chosen fits right in.

At the cost of almost no extra syntax, a whole range of things that would have required compiler plugins, special language features, or been flat-out impossible are enabled. It's (probably) a cheap win in this case.