3 Summarized linked content.
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This link discusses this question at length. I will IY"H when I have time write a short explanation based on it.   http://www.etzion.org.il/vbm/archive/9-parsha/13vayigash.rtf

Rash"i mentions (to answer for the opinion that there were girls born along with each of the sons of Ya'akov) that there were more females but they all died before going to Egypt. However, we are left with the implication that only those named and counted were part of the descending party. (. . which entails that all of Ya'akov's sons married Egyptian women, making it not remarkable when an Israelite man married an Egyptian woman later in the Torah, among other technical difficulties!)

Perhaps the number 70 is used not [only] as a census, but as a qualitative description of Ya'akov’s family for the purpose of comparing it in its totality to the nations of the world, which also comprise 70. (cf. D’varim 32:8-9) The reason Rash"u et al. were compelled to give an explanation for the absence of many females was that the inclusion of Dina and Serach indicated that women were being counted, despite the general rule that only males are counted when the Torah records census data. The burden of explanation is really on the inclusion of these two women, not the exclusion of all the others.

Thus, an alternative [to the null hypothesis] to explain their inclusion could be that the Torah wanted to add up to exactly 70, while fitting the pattern of each wife - Le'a and Rachel - having exactly twice the number of offspring as her slave - Bilha and Zilpa. These specific members of the family were chosen from among all the other females due to their special merits, as attested in the midrashim.

This link discusses this question at length. I will IY"H when I have time write a short explanation based on it. http://www.etzion.org.il/vbm/archive/9-parsha/13vayigash.rtf

This link discusses this question at length.   http://www.etzion.org.il/vbm/archive/9-parsha/13vayigash.rtf

Rash"i mentions (to answer for the opinion that there were girls born along with each of the sons of Ya'akov) that there were more females but they all died before going to Egypt. However, we are left with the implication that only those named and counted were part of the descending party. (. . which entails that all of Ya'akov's sons married Egyptian women, making it not remarkable when an Israelite man married an Egyptian woman later in the Torah, among other technical difficulties!)

Perhaps the number 70 is used not [only] as a census, but as a qualitative description of Ya'akov’s family for the purpose of comparing it in its totality to the nations of the world, which also comprise 70. (cf. D’varim 32:8-9) The reason Rash"u et al. were compelled to give an explanation for the absence of many females was that the inclusion of Dina and Serach indicated that women were being counted, despite the general rule that only males are counted when the Torah records census data. The burden of explanation is really on the inclusion of these two women, not the exclusion of all the others.

Thus, an alternative [to the null hypothesis] to explain their inclusion could be that the Torah wanted to add up to exactly 70, while fitting the pattern of each wife - Le'a and Rachel - having exactly twice the number of offspring as her slave - Bilha and Zilpa. These specific members of the family were chosen from among all the other females due to their special merits, as attested in the midrashim.

2 shorter URl, without using Google, for seemingly the same resource
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