They sell them because people will buy them....and because a lot of people can use them and not have a problem.
As with all things, use in moderation. I don't think the good doctor ever intended for people to be pigging out on low carb goodies or skimping on legal veggies so that they can have a bar or muffin instead. Low carb or not, if you find that you can't limit yourself to one or two servings of such foods a day (or less) and keep going back for more, they're probably a trigger for you and should be avoided. The fact that people tend to use these products in place of veggies is why I think they are better for later phases where you are already getting plenty of veggies and can afford to hold back a few carbs for a treat.
Sugar alcohols (maltitol, xylitol, sorbitol) do seem to stall a lot of people. OTOH, we usually only hear from those that have a problem, not from the ones that can use them successfully.
As always, YMMV.