Eating in the "sukkah" does not cause a parallel problem because many people simply enjoy eating outdoors in the shade of a "sukkah". Hence, seeing someone eating in a "sukkah" does not "per se" lead one to assume it is still "ḥol hamoed". Likewise, eating in the "sukkah" does not "per se" impinge on one's own celebration of Shemini Atzeret. Therefore, the prevalent practice is to eat in the "sukkah" on Shemini Azeret outside the Land of Israel, but not to recite the "berakhah" for sitting in a "sukkah", as reciting it would "impinge" on the unique status of Shemini Atzeret.