Because with nothing to compare it to, even the most idyllic peace means nothing. Through the knowing of harshness, people learn to appreciate the gentle; the knowing of war defines the knowledge of peace. There is no rainbow without the rain.

Brienne can have all the smiles she'd like. Why, look, here comes another one: the confirmation they're a good team has her grinning again.

More of her means there's more to love. Frea never comments negatively on Brienne's size. If things get awkward, they'll find a way around it and carry on. No big deal. No more than the fact Frea's so slight in comparison. Frea knows exactly what Brienne should do with her arms, or at least her hands: she should give them to Frea to hold because she's reaching for them. "That suit looks good on you. C'mon, let's put it to good use."