I come from on of those places back east where “most people never leave” and I’ll never go back for more than a visit. While SD is definitely more transient than many places there is a large and stable population committed to life here. It’s pretty funny but most people experience exactly what you have. The first three years, newcomers are excited to be here, typically renting and running around to all the fun places SD has to offer. They hold onto the identity of where they are from spending weekends at bars rooting for the Sox/Pats/Celtics, Yanks/Knick/Giants, Mets/Nets/Jets, Phils/Eagles/Sixers never truly embracing their new home nor trying to assimilate to life in a more diverse place than they came from. By diverse I mean everyone didnt go to the same school or grow up the same place. It becomes self selecting and most of the people you meet are in the same situation. Hence you think it is more transient than it actually is. After 3 years, people who are committed to staying begin to lay down roots and meet others who are equally committed. After that it becomes alot less transient.
My wife and I went through this ourselves and I have seen newbies go through this over and over again. Some make it and will stay forever….some don’t.