Question

Why does a user needs privileges over his own schema to create packages and triggers?

Answer 1

Are you asking why users need particular priviliges (i.e. CREATE TABLE, CREATE PROCEDURE, etc) in order to create particular types of objects in their own schema?

If so, the natural answer would be that good security begins with the principle of least privilege– that is, a user should only have those privileges that they truly need to do their job and no more. DBAs frequently want to create read-only accounts for users in the production database (business analysts, for example, often need to do different sorts of ad hoc reporting, developers may need access to troubleshoot certain types of problems, etc). If a user were always able to create objects in their own schema, those read-only users would suddenly be able to deploy code to the production database without going through change control or even necessarily testing anything. And that generally leads to a proliferation in code doing basically the same thing (i.e. a dozen analysts each have a procedure to calculate sales tax in their own schemas) but each of which has its own unique signature, logic, requirements, assumptions, etc. And heaven forbid that one of those analysts get fired because the DBA would naturally delete their account, only to find out that some crucial report depended on code that existed only in that analyst’s schema.