In his introduction to Yosef Lekach, Rav Eliezer Ashkenazi notes that a significant difference between Chanukah and Purim is that one is not required to celebrate Chanukah with a feast, per se. Since there were Jews still perishing in battle on Chanukah, we cannot institute a national feast. On Purim, however, the celebration requires both feasting and joy because not one single Jew died.
According to the Ben Ish Chai, we need both actions to celebrate both the spiritual renewal, and the physical safety.
The Sfas Emes emphasizes this by noting that, grammatically, the verse uses the word v’aso (“and he made”), implying that H-Shem made this into a day of joy and celebration.
R’ Yitzchak Hutner notes that any holiday from the Written Torah requires a degree of joy, as the Rambam (Mishneh Torah, Hilchos Yom Tov 6:18) makes clear. The holidays from the Oral Torah require drinking. Since this holiday contains aspects of both the Written and Oral Torahs, Purim requires both joy and feasting.