It’s in the name. “Epiphany“ means to reveal and for the Eastern Orthodoxy, it doesn’t just mean just the arrival of the Magi - it also means Jesus’ revelation as a teacher on the River Jordan. More emphasis is placed on Jesus being revealed to the world, particularly those who aren’t Jewish, whereas in the west, Jesus is the revelation of God to the Jewish people.
All Christians place some importance on the Magi and their miraculous arrival, but when you celebrate depends on whether you place more importance on Jesus as an embodiment of God or as an avatar of God.