Why?
I have a kidney disorder that causes me to waste potassium. Without a supplement, I can't get enough in my natural diet without eating like 10-20 avocados a day, or 6 cups of spinach.
A fun side effect of hypokalemia is that your muscles get really sore, like you just did a full body workout. So, you can literally feel when your potassium is low.
The low salt coincides with some of the most intense food cravings I've ever experienced. I don't crave foods high in potassium, however; just foods with a lot of regular NaCl. So, my body does its best to tell me I need to eat something, triggering a psychological compulsion to get it, but the compulsion is to eat the wrong thing.
I'm just one data point, but I think this might extrapolate out to more people than just me. If you're compelled to overeat, you might be missing some key nutrient that just isn't present in abundance in your current diet. The trick is finding out what it is.
Random related thought - awhile back there was a series of blog posts that got pretty popular (I can't remember the blog's name) trying to investigate the root cause of obesity. They settled on some odd conclusions, but one of the things they noted in their meta-analysis of extant obesity research is that places with lower obesity have more of a particular dissolved mineral (they asserted lithium was the root cause, but I didn't find their conclusions convincing) in their drinking water.
It could be that there are trace elements that, if you don't have mineral-rich drinking water, are otherwise hard to get from a standard diet that drive this craving behavior that I've experienced.
Then I asked my doctor to give me a different medicament, because I suspected a variation of a deficiency. Her answer was: I don't have experience with that medicament, but after four months she relented. One week later my craving was much, much less.
This experience astounded me extremely deeply.
I have come to the conclusion that there are some body processes, let's say instincts, that can go astray.
Compare this to drowning. Even if people know that there's only water, they try breathe. It's just too strong an instinct.
Having experienced this, I now respect obese people. They just have the bad luck that their instinct of eating derailed. Now they not only lost body fitness but also respect.