system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If our skin regenerates, why do scars last so long?

When I was five days old I had a major surgery on both my small and large intestines, which was followed by a colostomy. I am now seventeen and my scars are still clearly visible. I've always wondered scars stay visible for so long, even lifetimes, if our skin regenerates. (I've read that all the cells that make up your skin are new within a week.) So, why do scars remain. At that point aren't they unnecessary / redundant? Wouldn't it be more beneficial for the body to have smooth skin without scars, moles, or blemishes?
EDIT: Ok I kind of get it. I understand it takes a long time to heal, but there is not way the tissue isn't "healed" after seventeen years. I mean this scar is faded but its gonna be there for the rest of my life.  You explained that dermis takes larger to heal, but how long is that?
FOLLOW UP QUESTION: What determines how long a scar will last? Is it possible for doctors to minimize scaring or completely eliminate it when you go "under the knife"?
gpt
Skin scars occur in the dermis, which is the 'lower' level of the skin as opposed to the epidermis. At the deepest level of the epidermis, as opposed to the superficial layer we know as the surface of our skin, skin cells are reproducing constantly, and moving up through several layers while gathering keratin until they are dead  keratinocytes that get sloughed off in daily life. 

The abundance of tougher, single-direction collagen in a scar disrupts the growth pattern over that previous laceration. So imagine you've got water constantly bubbling up from a manhole, constantly flowing and then dispersing when it reaches the surface. These are your cells rising up through the layers then 'falling off'. Nail a stick across the opening of the man hole. Water continues to rise up and disperse, but can't go directly through the stick, and thus simply disperses around it. If anyone can imagine a better analogy or sees glaring flaws do feel free to tell me!