Purim
Question
Why no הלל on Purim
Answer
Shalom!
Thank you for your question.
There are a number of reasons why Hallel is not recited on Purim while it is recited on it’s “cousin” holiday of Chanuka.
One reason is that the miracle of Purim had no connection with the land of Israel. So too, the miracle of Purim did not lead to a complete freedom as the Jewish people were still living under Achashverosh’s' rule. Related to this idea is the general rule that we recite "Hallel" on the festivals which celebrate our freedom from Egypt. Hallel begins with the words, "Give praise, servants of G-d." Our recitation of Hallel at these times is to celebrate the fact that we are no longer "servants of Pharaoh," but rather we are "servants of G-d."
Another reason is that the reading of the Megillah serves in place of Hallel. According to this latter approach, one who is stuck without a megillah should indeed recite Hallel (but without the blessing before and after) although we do not pasken this approach le'hacha.