Translation:In winter, you wear warmer pajamas.
Given how literal many of DL's translations are, I can see that they would limit "During the winter" to «Pendant l'hiver».
In many respects, DL teaches translation not self-expression. I am not suggesting that is bad (or good). It's just my take on their process. The exercises aren't about how you or I would formulate a thought; it is about how an experienced translator would re-write a French sentence into English (or visa versa).
For me, it helps to look at their methodology thru this lens. Everyone's mileage will vary.