Why the owner of a database can't alter the tables of this database that are owned by other owners?

For now I don't understand why this access rights segregation exist. Is it implemented for some security reasons? Or can it be needed by some use cases I can't imagine right now? Knowing almost nothing about the reasons behind concrete PostgreSQL design I wonder why prevent a database owner from altering those tables of the database owned that are owned by other owners. Here's what [the official documentation on altering tables](https://www.postgresql.org/docs/10/static/sql-altertable.html) says regarding who can alter tables of a database: > You must own the table to use ALTER TABLE. Of course I don't argue the design or the documentation. I'm just wondering why it can be needed to limit a database owner that way?