Why mention to Oracle ?

Why PostgreSQL DOCs needs to show or compare the Oracle way of doing things
?

I understand that on page Porting from Oracle PL/SQL is ok to mention
Oracle, but there are other places where it's not needed. Or, if it's ok to
mention, why not mention SQL Server or MySQL or any other ?

Bug Reporting Guidelines
Especially refrain from merely saying that “This is not what SQL
says/Oracle does.”

LOCK
the PostgreSQL lock modes and the LOCK TABLE syntax are compatible with
those present in Oracle.

SELECT
Applications written for Oracle frequently use a workaround involving the
automatically generated rownum column, which is not available in
PostgreSQL, to implement the effects of these clauses.

ROLLBACK TO SAVEPOINT
The SQL standard specifies that the key word SAVEPOINT is mandatory, but
PostgreSQL and Oracle allow it to be omitted

Data Type Formatting Functions
FM modifies only the next specification, while in Oracle FM affects all
subsequent specifications, and repeated FM modifiers toggle fill mode on
and off.

Data Type Formatting Functions
A sign formatted using SG, PL, or MI is not anchored to the number; for
example, to_char(-12, 'MI9999') produces '- 12' but to_char(-12, 'S9999')
produces ' -12'. (The Oracle implementation does not allow the use of MI
before 9, but rather requires that 9 precede MI.)

regards
Marcos