That's Racket's primary feature. Making a new language in Racket is just writing some functions (and macros, which in Racket are a kind of function). This mean

That's Racket's primary feature. Making a new language in Racket is just writing some functions (and macros, which in Racket are a kind of function). This means pretty much all your tooling comes along for free (syntax highlighting, debugger, etc). The reason that someone might write a DSL is because it better fits the problem. The OP's example Pollen for instance, provides an easy way to run a full programming language to produce HTML output, something that can be tedious without language support.