[Python] Why can't private attributes of Pydantic be mutable objects?

I used the following line of code

_missing_attributes: list[str] = PrivateAttr(default_factory=list,)


The following error occurred and I don't understand why

File "/home/**/.venv/lib/python3.12/site-packages/pydantic/dataclasses.py", line 255, in create_dataclass
cls = dataclasses.dataclass( # type: ignore[call-overload]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/dataclasses.py", line 1268, in dataclass
return wrap(cls)
^^^^^^^^^
File "/usr/lib/python3.12/dataclasses.py", line 1258, in wrap
return _process_class(cls, init, repr, eq, order, unsafe_hash,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/dataclasses.py", line 994, in _process_class
cls_fields.append(_get_field(cls, name, type, kw_only))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/dataclasses.py", line 852, in _get_field
raise ValueError(f'mutable default {type(f.default)} for field '
ValueError: mutable default <class 'pydantic.fields.ModelPrivateAttr'> for field _missing_attributes is not allowed: use default_factory

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