I think because the Makedonian kingdom was more contiguous than the other successor states; it was still ruled by the Argeades clan, who were the original rulers of the Makedonian kingdom.
Actually, the Argead line died out with Alexandros IV, after he was murdered on orders of Kassandros. The rulers of Makedonia during this time are the heirs of Antigonos Monophtalmos, a Makecedonian commander under Alexandros.