Do Morrocan-stye pickled lemons really need 5 to 10% salt?
As I understand it, you may be seeing some confusion between two very different processes.  When making sauerkraut, you are fermenting cabbage in brine, and the fermentation gives sauerkraut its characteristics.  I believe this means you need to have or introduce the right microbes, and give them time and space and the right environment to work, and prevent oxidation (keep it submerged), especially since you need access to the air to vent the gasses being produced, things like that?

Pickling, at least these kinds of (brine?) pickles, are not the same thing.  To make this sort of pickle, you are steeping the food in a sterilizing brine, one high in acid (usually vinegar) and salt and sometimes other preservatives, and all sorts of things that microbes don't like.  The changes that happen are nothing more than the food steeping in the brine, and osmoisis-ing the brine and food into equilibrium.  The food doesn't even have to age much in pickling - it gets the most flavor into the food, but there are shortcuts (like chopping smaller or making various "quick-pickle" recipes) which is simply not possible with fermented recipes.

The point is, fermentation preserves, it keeps food from spoiling, by using friendly microbes to out-compete the microbes that spoil the food.  Brine pickling intends not to let any microbes grow, because the pH is too low, the salt is too high, the environment is generally not microbe-friendly.  Fermentation is fussier (needs lots of variables right), but it is also transformative.  Brine pickling is easier, but also tends to produce much stronger flavors (especially at preservation strength).

At some point, I think, "fermented pickles" became a term, or the results of fermentation were also referred to as being pickled and the terms overlapped, or something - and certainly you can ferment lemons, if using much less salt (especially given your commenters' mention).  But judging by the recipes I saw, it looks like the Moroccan preserved lemons your source quoted at 5-10% salt are simply preserved, not fermented - left in a brine with salt and acid, which were intended to keep the food unspoiled.  So the problem may be that you're mixing up two very different preserving methods, that happen to be a little bit similar and are for some confusing reason called by identical names.