https://www.israelnationalnews.com/news/387377
An opinion of our Sages teaches that the evil decree in the Purim story came when the Jews of Shushan attended the feast of Achashverus which celebrated his false understanding that the Jews would not return to Eretz Yisrael to build the Beit Hamikdash. Apparently, Mordechai was the only Jew who protested. He begged the Jews not to participate, but they were happy to attend, insisting that the food and drink would be glatt kosher.
The cause for the celebration – the belief that the Jews were freed of the obligation to return to the Land of Israel and to rebuild the Beit HaMikdash did not seem to bother anyone save Mordechai. There is no record that the other great Rabbis of the time, of which there were many, supported Mordechai’s vehement protest. Perhaps they dd and perhaps they erred and attended the gala party which celebrated the disconnection from Eretz Yisrael and an open door to acceptance amongst the Gentiles and assimilation, believing it would cement good relations with the powers that be.