I did the expat thing for just under two years. Leaving behind your old life isn't the least bit appealing if you like your old life. If you don't like your old life due to temporary circumstances, then you'll go back home after a few years when circumstances change. IME, the people who stay significantly longer than that have more internal problems than external.
It's also possible that they're either more interested in deeply exploring another culture or simply more flexible than those who spend nearly their entire lives in one culture are.
It certainly is possible, but in my experience not very common. The long-term expats tended to stick to the expat community, which was mostly about creating a tiny bubble of "home" in the host country. Or at least a television-inspired approximation thereof.
The ones who really did want to explore and immerse themselves in another culture usually did that for a few years before moving on to explore another culture.
