I think it's due to a combination of factors which all come down to a less favorable environment for factories (unions/higher wage expectations, regulations etc

I think it's due to a combination of factors which all come down to a less favorable environment for factories (unions/higher wage expectations, regulations etc). However, a weaker dollar can mean more factories stay here for competing cheap labor. The trade-off is less spending power, which means our economy must shift away from being spending based. People will kick and scream when that realization hits but America simply won't continue to dominate the world economy.