אֵ֣ת ׀ שְׁתֵּ֣י הָעֲגָלֹ֗ת וְאֵת֙ אַרְבַּ֣עַת הַבָּקָ֔ר נָתַ֖ן לִבְנֵ֣י גֵרְשׁ֑וֹן כְּפִ֖י עֲבֹדָתָֽם׃
他把兩輛車和四頭牛交給革順的子孫，按著他們的職務分配。
Rashi
כפי עבדתם [TWO WAGGONS AND FOUR OXEN HE GAVE UNTO THE SONS OF GERSHON,] ACCORDING TO THEIR SERVICE — only two wagons and four oxen, whilst the sons of Merari were given twice as many, because the burden of the sons of Gershon was lighter than that of the sons of Merari since they carried the boards, the columns and the sockets.
Chizkuni
את שתי העגלות, “the two wagons, etc.” seeing that the weight of the curtains and skins for the roof, and other incidentals, were relatively light, only two of the wagons were assigned for that task.