During this period of body initiated fasting, or ketosis, normal energy stores (glycogen) are mostly depleted in 12-16 hours, and completely depleted in a few days. At that point the body goes into an accelerated healing process known as autophagy where the most superfluous tissues begin to be removed from the body. And what are the most superfluous tissues? The pathologic diseased ones. The dysfunctional ones.
Autopsies on people who have starved to death show that the most critical tissues, brain, eyes, and the like, are spared right up to the point of death, and there's a logical natural reason for this: if one is close to death from starvation but does survive, when health is regained all critical facilities remain intact. Showing, in only one of so many ways, our body's innate intelligence knows exactly what it's doing.
Therapeutic water only fasting, BTW, is not starvation, not even close to it. Starvation does not occur until all fat stores are depleted, whereupon proteins (body structure) begin to be converted to fuel. When there is progression from ketosis to starvation any further lack of caloric intake is no longer therapeutic and becomes dangerous.
Fat is consumed for fuel in ketosis because fat is the most plentiful source of stored energy in the body. So pathogenic tissues are removed, new healthy tissues are generated, and fats stored in the body are used as fuel for that process. Glycogen stores are completely depleted in a few days, stored fats in all but the anexoric will provide sufficient energy for the autophagy process to continue for several weeks and even longer.
This is a good point to mention that extended water only fasting should not be done without medical supervision. Intermittent water only fasting is usually OK, up to 24 hours, no more than once a week. The problem with finding medical supervision of water fasting is the number of MDs who have any training (much less practical expertise) in fasting supervision is very limited. More and more MDs are beginning to learn of the immense leverage fasting introduces in health recovery as the studies are coming at a rapid clip recently, but it is not common knowledge yet. And it also bears mentioning widespread fasting expertise among MDs may be a long time coming, as far greater revenues (and with much less effort) can be achieved prescribing minimally effective (or even counterproductive) drugs.
So does the body want to be in ketosis? Probably not until very ill or injured, when there is a lot of healing to be done, and then the body "forces" the condition of ketosis, rather than being "consciously chosen".
In addition, primates (including humans) instinctively chose carbohydrates for foods (when available) over fats. Thus ketosis in not our natural condition, it's the emergency back up survival system. Without which, BTW, we as a species would not still be here...so it is not superfluous, it's just not primary.
Consider if you will a thought experiment to illustrate: you're lost in the woods for a week and really hungry. All the sudden you come across a big fruiting apple tree with low hanging ripe apples and chickens on the ground pecking at the fallen apples. Would you pluck and eat the ripe apples hanging from the branches, or catch a chicken first? If you think "chicken", consider the following: you are freaking hungry! It's takes mere seconds to begin eating all the (incredibly delicious) apples you want, but the chicken you have to catch, then begin eating it...raw? Tearing it's flesh with the claws (you don't have)? Ripping into its muscles and organs with the rows of razor sharp teeth (you also don't have)? Or gather the wood, build a fire, cook the chicken?
Right, you'd eat the frickin apples.
In this brief vid Dr Davis talks a bit about his experience putting patients into ketosis for fat loss surgery, and recommends a few books he's currently reading, one of which sounds very interesting to me: "The Idiot's Guide to Plant Based Nutrition".
https://www.amazon.com/Plant-Based-Nutrition-2E-Idiots-Guides/dp/1465470204/ref=dp_ob_title_bk
And here is Dr. Davis: