Oznayim la'Torah: Because it is correct for the owner to stand by his Korban whilst it is being sacrificed, as the Gemara states in Sotah, 8a.

Rashi: Because Hashem was not accustomed to appearing to him by day. ¹

Seforno: Because he was not on the level of Moshe, who, once he was established, was assured of Hashem's attention at any time. ² And he figured that perhaps Hashem would come to meet him, like He came to meet Moshe when he first became a prophet. ³

Rashi and Targum Onkelos: It means 'He went alone'.

Rashbam: It means It means 'He went limping', ¹

Targum Yonasan: It means 'He went doubled-over ² like a snake'. ³