My take on it is that often when folks arrive here, they've just been diagnosed and when they start "low carbing", they are lower carbing for them, but not really low carbing. How many people say they couldn't give up x, y or z, then spend time testing every permutation before eventually giving in.
Secondly, for those who don't keep accurate records, they could be unlikely to pick up on some of the sneaky carbs we all encounter from time to time, and also some foods, like leafy veg, do have carbs, and if eaten in enough quantity (to fill up, for example), it'll all add up.
And finally, some people's systems will hang on very hard to the higher levels by liver dumps, false hypos (people sometimes treat), and even the odd meandering off the wagon.
This thing is hard. There's a lot to get our heads around, and some people's personal circumstances make it hard to make a hard switch immediately and stick with it. Those who have resistant partners or families have a particularly hard time, in my view.
There are many ways to skin this cat. What matters is folks get there in the end.