Another interpretation: Why did he weep? Because he saw people whispering, saying to one another: Has this man come to introduce among us some matter of lewdness? For ever since the world was stricken by the Flood, the nations of the world fenced themselves off from sexual immorality. And this teaches that the people of the East were fenced off from immorality.
Jacob Wept Lest the Easterners Suspect Him of Immodesty
Yalkut Shimoni on Torah 124:6
דָּבָר אַחֵר, לָמָּה בָּכָה, שֶׁרָאָה בְּנֵי אָדָם מְלַחֲשִׁין, אָמְרוּ אֵלּוּ לְאֵלּוּ וְכִי מַה בָּא זֶה לְחַדֵּשׁ עָלֵינוּ דָּבָר שֶׁל עֶרְוָה שֶׁמִּשָּׁעָה שֶׁלָּקָה הָעוֹלָם בְּמַבּוּל גָּדְרוּ אֻמּוֹת הָעוֹלָם עַצְמָם מִן הָעֶרְוָה, וַהֲדָא אָמְרָה שֶׁבְּנֵי מִזְרָח גְּדוּרִים מִן הָעֶרְוָה.