I am not sure from where you are getting the sense that the Antigonid dynsaty (the Hellenistic rulers of Macedonia) was more numerous than the Seleucids or Ptolemies in the 3rd century. A brief look at some online sources give the following numbers:

• There were 5 different Seleucid kings in the 3rd century.

• There were 5 different Ptolemaic kings in the 3rd century.

• There were 5 (arguably 6) different kings of Macedonia in the 3rd century.

Is there a specific source or issue that you had in mind when asking this question? Or perhaps are you referring to the dynastic struggle that occurred in the early 3rd century BCE in between Cassander and Demetrius I, or the subsequent struggle between Antigonus II, Pyrrhus, Ptolemy Keranous, and the Galatians in the 280s? While these conflicts led to some dynastic instability, eventually Antigonus was able to re-install himself as king and stabilize his dynastic claim to the Macedonian throne.