וַיַּרְא֙ חֹתֵ֣ן מֹשֶׁ֔ה אֵ֛ת כָּל־אֲשֶׁר־ה֥וּא עֹשֶׂ֖ה לָעָ֑ם וַיֹּ֗אמֶר מָֽה־הַדָּבָ֤ר הַזֶּה֙ אֲשֶׁ֨ר אַתָּ֤ה עֹשֶׂה֙ לָעָ֔ם מַדּ֗וּעַ אַתָּ֤ה יוֹשֵׁב֙ לְבַדֶּ֔ךָ וְכָל־הָעָ֛ם נִצָּ֥ב עָלֶ֖יךָ מִן־בֹּ֥קֶר עַד־עָֽרֶב׃
Ketika mertua Musa melihat segala yang dilakukan Musa terhadap umat itu, ia berkata, “Apakah yang kaulakukan terhadap umat ini? Mengapa engkau duduk seorang diri, sementara seluruh umat berdiri di sekelilingmu dari pagi sampai petang?”
Chizkuni
אשר הוא עושה לעם, “what he was doing to the people.” They were making one another impatient. On the one hand, the common people were forced to stand in line most of the day waiting for their turn. On the other hand, Moses was becoming more and more weary having to deal with so many disputes.
Rashbam
מדוע אתה יושב לבדך?, and as a result of your being the sole judge the entire people have to stand in line before you from morning to evening.