Because not every diet suits every person? If it did we'd all be doing the same one
Things people love about SW, other people dont. Same goes for WW, the things I love about it, probably put people off. Its a case as always of finding which one fits you best, therell always be 'new' diets as long as there are overweight people
And don't forget not every diet works for every person. I know I cannot eat lots of carbs and lose weight. It really is as simple as that! I learnt this many years ago. I ahve tried to ignore it over the years following both SW and WW. But it will NOT work whilst I eat more than jsut a very small amount of carbs. I am doing WW now, but know that I always have to do low carb too. We are all built differnetly. If you can follow SW and lose weight effectively, just count yourself lucky and enjoy!!
You are not necessarily being asked to cut out complete food groups. You do the attack phase (protein only for between 2 and 10 days) you then introduce protein and veg for a few days and then alternate, very similar in some respects to red days on slimming world. Even ww has a version of it now, high protein low fat.