Racket DSLs aren't the same as 'spinning up a new lexer' at all.
Making DSLs is hard, and being a PLT expert does not make one an expert at language implementation. Those are completely different skills (see Brady's reimplementation of Idris on Chez Scheme and the reason for it).
Racket allows people with new ideas to prototype them efficiently by easily implementing a compiler that would've been an interpreter otherwise.