Why did the wolf pack in Twilight go shirtless?

In the twilight saga, when the wolves transform, their clothes get ripped and teared as their body's take the new shape. So instead of wasting a shirt, they don't wear one. In one of the books, one of the wolves state that ripped shoes were becoming a problem, so they often didn't wear shoes either. You will see that Jacob has his pants folded and strapped to his ankle to wear when he transforms back into a human.

Hope this helps!