Hermione was bored. Painfully bored. And when she got bored, she grew sullen and depressed. When she used to grow restless, her teacher would set her a seemingly impossible task to keep her occupied. He attempted the same a few times after they were married with little success. Instead, he would gift her a new volume on spells or potions to perfect. Antonin practically built her a library with all of the books he found her when she was bored. She could've used them too.