Forty years of leadership were no sinecure for Moses. The people complained, Korach and company complained, and even Moses’ own siblings complained: “And Miriam and Aaron spoke against Moses because of the Cushite woman whom he had married” (Num. 12:1).
Who the Cushite woman was exercises many of the commentators. One possibility is that it was Zipporah, who came from Midian, which is also known (Habakkuk 3:7) as Cushan.
Or maybe what Miriam and Aaron meant by a Cushite woman was an Ethiopian, since Cush generally denotes Ethiopia (as at the beginning of the Book of Esther); if so, the woman was someone else than Zipporah and was a second, South Egyptian wife.
But in neither case did Miriam and Aaron complain about Moses’ choice of a wife, but about the way he treated his marriage.
What was their problem? According to Rashi, it was that he had separated himself from his wife; when Zipporah heard that Eldad and Medad were acting as prophets (Num. 11:27), she said, “Woe to the wives of these men if they have anything to do with prophecy, for they will separate from their wives just as my husband has separated from me!”
In Avot d’Rabbi Natan, Rabbi Shimon ascribes to Miriam and Aaron a similar comment, “Since he (Moses) is so overweening (priding himself on reaching prophetic heights), he has separated himself from his wife!”
The implication of both comments is that a person in public life, like Moses, must not sacrifice his or her marriage and family life for the sake of the community.
Why, then, does the Torah not spell out the facts of the episode?
Presumably because even when critics are making a valid point, as Miriam and Aaron may well have been doing, they have to exercise restraint in disparaging a spiritual leader. Even if it is their own sibling!
Though he was their brother, Moses was still the God-appointed leader and his own family was not exempt from treating him with respect.