John Romer says, in Testament: The Bible and History, page 129, under the Syrian kings, the position of High Priest was on sale to the highest bidder. The High Priest was the virtual ruler, under the Syrian king, of all Judah. It appears here that Jason had bought the position of High Priest and "received from Antiochus permission to convert Jerusalem into a Greek polis called Antioch". But then Menelaus bribed Antiochus and was appointed High Priest in place of Jason.
2 Maccabees 4:27 tells us that Menelaus, a totally disreputable person, had not paid the money he had promised the king, but then (4:32) stole gold vessels from the temple. After a period of turmoil, Menelaus managed to remain in office, increasing in wickedness:
2 Maccabees 4:50: But Menelaus, thanks to the covetousness of the men in power, remained in office, where he grew in wickedness and became the chief plotter against his fellow citizens.
Whether bitter at having bought the office of High Priest and then losing it, or anxious to remove a person misusing the office, Jason could do nothing while Antiochus was alive. However, rumours of Antiochus' death encouraged Jason to attack Jerusalem and regain the lucrative position.
This account may be read with some caution because 2 Maccabees differs in some places from 1 Maccabees and can be regarded as a political document rather than a literal history. Robert Eisenman says, in The Dead Sea Scrolls and the First Christians, page 39, 2 Maccabees seems to have been written to correct the portrayal in 1 Maccabees of Judas Maccabee and of the Hassidaean movement he headed.