Have you ever wondered why scar tissue seems to have so many issues in the Sun with sunburns and doesn't seem to be able to grow hair?
As it turns out, the lack of pigmentation in your scar tissue makes scarred regions very susceptible to sunburn and other Sun radiation-invoked issues. For this reason, you really need to be careful to cover your scars if you're out in the Sun for long periods of time.
The severity of lacking pigmentation depends highly on how deep the wound is. The deeper the wound, the less melanin is going to be present in the pigmentation. The shallower the wound is, the more you should have. Melanin plays a big role in how Sun-friendly your skin is.
So why no hair? - Again, this is a phenomenon that can only be explained by the depth of the scar. The deeper the cut, the less likely you're going to be able to regenerate hair follicles in that area.