There is always a duplication of "schema", both your database and application language need a definition of this. Why can’t an application just run SQL queries

There is always a duplication of "schema", both your database and application language need a definition of this. Why can’t an application just run SQL queries directly against the database? I agree that there are many reasonable ways to manage a database, but not all of them involve reproducing the entire schema directly in client code the way an ORM does.