Why splitting logic between Postgres and an application considered worse than splitting it between multiple micro-services? A DB is a storage service with INSER

Why splitting logic between Postgres and an application considered worse than splitting it between multiple micro-services? A DB is a storage service with INSERT/SELECT/e.t.c. as an API. Why we cannot extend this API to include stored procedures too? Indexes are commonly used to enforce data integrity. Why we cannot use triggers to do this even better?