Because they obviously know better. [Even Hermione won't let her curiosity take her to a deadly outcome.]

Hm that's a good idea. I don't really see a problem cutting out holes for them and it's not like I have anything to hide on my back.

[She's more concerned about hiding a certain word carved into her arm.]

When Winter comes, I'll deal with keeping warm somehow. I am fairly talented when it comes to creating flames.