The קרובץ לפורים is on every Bracha of the שמונה עשרה except on the Bracha “את צמח”.
Some claim the reason for this is, "All the wars were fought by מלכות בית דוד except for מלחמת עמלק which were fought by the grandchildren of Rochel. Mordechai was מתקן for Shaul Hamelech's war on אגוג. Therefore we don’t mention the נס when saying "את צמח דוד ."
The truth is, קרובץ, were written not only for Purim.There are קרובץ for Hoshana Rabah,17th Tamuz, 10th Teves, and 9thAv. They all have no קרובץ on את צמח.
The פייטן for קרובץ was R, Elazar b Hakalir. In his פיוטים, he generally follows the Yerushalmi over Bavli.
According to the Yerushalmi, the Bracha of את צמח and וירושלים עירך, are combined into one Bracha.
Hence, no קרובץ for את צמח