Recital 5
EU GDPR

(5) The economic and social integration resulting from the functioning of the internal market has led to a substantial increase in cross-border flows of personal data.

The exchange of personal data between public and private actors, including natural persons, associations and undertakings across the Union has increased.

National authorities in the Member States are being called upon by Union law to cooperate and exchange personal data so as to be able to perform their duties or carry out tasks on behalf of an authority in another Member State.