And that is not true. It is a claim of 19./early 20. century historians, that all diadochs except Seleukos divorced from their persian and median wifes. There is not a single ancient source, which is making such a claim.
- As probably literally anyone on this site could tell you, the Seleucids were a Hellenistic dynasty like the Ptolemies. However, unlike the Ptolemies, they did have partial native ancestry; specifically, Antiochus I Soter was half-Iranian on his mother's side. Incidentally, Seleucus was the only groom from the Susa weddings who did not divorce his Persian wife after Alexander's death (except Hephaestion, but he was a bit too dead to divorce anyone), which says a lot about the attitude of Macedonian nobility towards foreigners (Alexander himself had issues because his mother was an Epirote, and they're at least Hellenic).
THE SUSA MARRIAGES — A HISTORIOGRAPHICAL NOTE on JSTOR
Thats a conclusion made by conflating their own societal norms with the norms of the hellenistic period. For example there was no need to get divorced as the macedonian nobility wasn't monogamous. You could marry other women, if you got a political bonus from it or were really in love. It was accepted to have a second wife. Why get your support in danger as Diadoch by insulting the local persian-median nobility?
Examples: Philipp II or Pyrrhus
What's right, is that the Seleucids were better in making good diplomatic relationships with their near eastern neighbours by wedding diplomacy (for example Pontos, Armenia, Maurya Empire).