I'm sure we are all familiar with the famous gematriya equivalence i.e that barukh Mordechai (בָּרוּךְ מָרְדָּכַי) and arur Haman (אָרוּר הָמָן), is exactly 502. The question we need to ask is why the number comes out exactly 502.
The answer comes from the story of Ruth. We know that Ruth in gemetryia is 606 because she started off with 7 Noachide mitzvot, then added 606 when she converted. In the same manner, since drinking on purim is כְּנֶגֶד the full 613 mitzvot you'd think בָּרוּךְ מָרְדָּכַי, etc. should be equal 613. Instead, the gemetrya is only 502 -- we're missing 111.
111 happens to be the gematryia of אנס, so when the megilla says והשתיה כדת אין אנס, it means that it looked like the drinking was leshem mitzvah, but in reality we were missing the key component that made it kodesh, and so that is why the chachamim didn't go to the mishteh.
Still, the fact that the Jewish people refrained from having kiddush clubs for a fully 180 days was a serious problem, which is why Mordechai was metaken drinking on Purim ledorot. That is why we have the saying that "Hashem considers people who get drunk on Purim to be as great as Tzaddikim who stay drunk all year round".