Someone said a dvar Torah on this at my shabbos table. i dont remember the source offhand tho. The answer he said was that at the beginning of the machlokes, the wives of the men involved in the machlokes did not approve or want to participate. Their husbands were suspicious of this, and accused their wives of znus with Moshe. They went through the process of Isha Sotah, and were found innocent. The bnos Tzlofchad were backing up their claim by saying that their father wasnt involved in adas korach, or else their mother wld have gone through sota and been given a bracha of sons. being that there were no sons, he wasnt part of adas korach.
i personally still wasnt completely satisfied with this, because it was still repetitious, but we came up with the comparison to Chana, who ‘challenged’ Hashem to give her a son, or else she’d put herself in the position of sota and go through the process to be proven innocent and been bentched with a child….