Question about the alliance/treaty between Attalus I Soter and Antiochus III

Mar 2018
Almaty, Kazakhstan
When the Seleucid general Achaeus, the governor of Seleucid Anatolia declared himself king, Attalus I king of Pergamon allied himself with the rightful heir Antiochus III to defeat Achaeus who was a long time rival of Attalus. The 2 kings succeeded, but Attalus lost most if his territory to Antiochus after the victory and was only left with Pergamon and the surrounding areas.

How come Attalus who ruled from Ionia to the Taurus mountains lost most of his territory after HELPING Antiochus in his war against Achaeus.
Jan 2009
After looking at the timeline quickly:
228 Attalus gains control of Asia Minor.
223-221 Achaeus reconquers Asia Minor for Seleucids, but revolts some time after.
218 Attalus makes some gains.
217 Achaeus pushes Attalus back again.
216 Antiochus crosses to Asia Minor and defeats Achaeus. Attalus is allied with Antiochus.
213 Achaeus is betrayed and killed.

The reason why Antiochus doesn't give Asia Minor back to Attalus is because it was Seleucid territories anyway, which Attalus had conquered briefly about a decade prior. In short, Attalus had ALREADY lost those territories back to Achaeus/Seleucids prior to the alliance.

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