Qs re Barcelona "short timers" and smoking

Hi. I'm considering expatriating from the US to Barcelona. From what I've seen so far, it seems to me (and I could be wrong) that expats move to Barcelona, but they don't stay very long. Is that close to the mark? If so, what are some of the reasons they leave? And how does this level of transiency compare with other expat destinations?

About how long do expats stay, on average? It would be a bit unsettling to make a lot of good new friends in Barcelona only to have to wish them farewell a short time later.

Also, I was wondering if smoking is prohibited in Barcelona in public places, particularly restaurants and bars. How about when the business has some of its seating on sidewalks? Gracies/Gracias!