It would make a lot of sense behind-the-scenes-wise (back in '76, when this was being concieved) for "Obi-wan" to be his Jedi name, possibly being taken once he attained the rank of jedi knight. I say this because the jedi are clearly heavily based on samurai, & it was common practice for samurai to take on a new name any time they were promoted in rank, or had a major life-changing event. In fact, they'd often have gone by 4 or 5 different names by the time they died, though close friends & relatives would often continue calling them by their old "first" name. (i put "first" in parenthesis b/c japanese use the surname first, followed by the personal name; i.e. John Smith would be Smith John in Japanese). So, it's logical to assume that his birth name was Ben Kenobi, but at some point in his training, he was renamed Obi-wan, & this is how most people knew him b/c that's the name he went by when he became famous int he clone wars. Perhaps when he went into hiding on tatooine, he decided to use his birth name for whatever reason. Maybe he figured the few locals he came into contact with would know who Ben Kenobi was, but there might be a stronger chance they'd heard of Obi-wan Kenobi due to his high status in history.
It would make a lot of sense behind-the-scenes-wise (back in '76, when this was being concieved) for "Obi-wan" to be his Jedi name, possibly being taken once he attained the rank of jedi knight. I say this because the jedi are clearly heavily based on samurai, & it was common practice for samurai to take on a new name any time they were promoted in rank, or had a major life-changing event. In fact, they'd often have gone by 4 or 5 different names by the time they died, though close friends & relatives would often continue calling them by their old "first" name. (i put "first" in parenthesis b/c japanese use the surname first, followed by the personal name; i.e. John Smith would be Smith John in Japanese). So, it's logical to assume that his birth name was Ben Kenobi, but at some point in his training, he was renamed Obi-wan, & this is how most people knew him b/c that's the name he went by when he became famous int he clone wars. Perhaps when he went into hiding on tatooine, he decided to use his birth name for whatever reason. Maybe he figured the few locals he came into contact with would know who Ben Kenobi was, but there might be a stronger chance they'd heard of Obi-wan Kenobi due to his high status in history.