He says that compiler theory gives programmers the tools to solve problems with complex input. Building a parser for a Polish notation calculator can be tackled by a first-year CS student. But building an (correct) XML/JSON parser requires an understanding of AST.

So a programmer without an understanding of compiler theory cannot hope to process input that is not structured in the most trivial manner. The bulk of programming beyond CRUD apps require handing complex input, thus benefit from an understanding of compiler theory.