People renouncing citizenship don't do so simply because they've made a life for themselves in Europe or somewhere similar (be it temporarily or semi-permanent or permanent). Being a dual citizen has many advantages. (Not the least of which is allowing the US constitution to actually apply to you as you enter the country)
People renounce their citizenship when retaining it becomes more effort than the benefit received. For instance, I'm dual Italian-Canadian, and I have no qualms about retaining my Italian passport indefinitely, even though my father was Italian and I only lived in the country for a year.
Now, should the Italian government decide they needed monthly bank statements from my Canadian accounts like the US does, making my life a nightmare of paperwork every year, I might reconsider.