Why the main foreign policy partner of Russia in the X centuries. was Byzantium?

In 988, after Vladimir and his retinue laid siege to Chersonesos, Byzantium went to negotiations with him, the result of which was the signing of a union treaty. Under this agreement, Vladimir pledged to lift the siege and accept Christianity, in turn, Byzantium paid a large indemnity and gave Princess Anna to his wife. In fact, this was the main reason that in the 10th century the Byzantine Empire was the main trade and political partner of Kievan Rus.