SMS was an after thought long before .@ started. Tweets starting with @ weren't treated specially, and replies weren't yet a thing. Then Twitter started hiding

SMS was an after thought long before .@ started. Tweets starting with @ weren't treated specially, and replies weren't yet a thing. Then Twitter started hiding tweets that started with @ and there was a good amount of backlash from people complaining that this would reduce their ability to discover other interesting accounts by seeing who the people they follow interact with. Twitter however stuck with it and then the .@ convention started as a workaround. Now they are just going back to that original behavior except replies are an actual thing now so they can differentiate tweets that simply start with a @ from those that are actual replies, which couldn't be done when this change was first introduced.