User attribute choices not saved in order record

I've created two custom store line-item types, each with a few product attributes (/admin/commerce/config/line-items)

They show in the "Add to cart" form on my two display nodes. How do you record the attribute choices of the custom? If they choose a value and add-to-cart, it's not saved on the final order. How would you record the "xl", "blue" or "monogram 'abc'"?