John Gill Commentary Genesis 29:31

"And Jehovah saw that Leah was hated, and he opened her womb. But Rachel was barren." — Genesis 29:31 (ASV)

And when the Lord saw that Leah [was] hated
Not properly and simply hated by Jacob, as appears by his doing the duty of a husband to her, but comparatively; she was less loved than Rachel: and there are many things to be said for it; she was not beautiful as Rachel was; she was not Jacob's choice, as she was but imposed upon him through deceit, and he was forced to marry her, or he could not have Rachel his beloved wife: but the Lord had pity on her, and that she might have a share in her husband's affections, he opened her womb ;
or gave her conception; as Onkelos paraphrases it: but Rachel [was] barren ;
bare no children as yet, and for many years after, (Genesis 30:22–24) .