Timestamp should not change on alembic upgrade

Question

I just ran an alembic upgrade on my postgresql db. The diff between "before" and "after" revealed that all tables were rewritten despite the fact that only some tables were modified. The change occured only in the datetime column like so:

< 202   dac1d06a-e9e1-4739-a80c-9ae913e345c3    2023-05-23 12:05:58.972111+00   199 \N  139 \N  dut001  f   \N  script  initial commit  f
< 203   410ced4d-e2cf-4006-8cf0-f143f744f953    2023-05-23 12:05:58.980174+00   199 \N  141 201 duthandler  t   \N  script  initial commit  f
> 202   dac1d06a-e9e1-4739-a80c-9ae913e345c3    2023-05-23 14:05:58.972111+02   199 \N  139 \N  dut001  f   \N  script  initial commit  f
> 203   410ced4d-e2cf-4006-8cf0-f143f744f953    2023-05-23 14:05:58.980174+02   199 \N  141 201 duthandler  t   \N  script  initial commit  f

The tables were initially generated via sqlalchemy:

class MyClass(Base):
    __tablename__ = "alias_map_expanded"

    seq2 = Sequence(name="seq2")
    id = Column(
        BigInteger, sumo_seq2, server_default=seq2.next_value(), primary_key=True
    )
    uuid = Column(
        UUID(as_uuid=True), server_default=func.gen_random_uuid(), nullable=False
    )
    creation_date = Column(
        DateTime(timezone=True), server_default=func.current_timestamp(), nullable=False
    )
    ...

Now I already read about naive and non-naive timestamps and got an idea on how to get from one to the other in python, but I am really stuck with the question why that even happens during the upgrade and how to avoid having the timestamps changed all together.

Thanks in advance!