I don't think the reasons are just for economic freedom - NE states are heavy on gun control and NYC is the place where they freak out over a soda, but personal and corporate taxes are much lower in the South and the weather is better.
The article didn't mention California, but that state is flat-lining - people are leaving that state in droves, last census they gained no new Congressional seats for the first time in many decades. Illegal immigrants and Moonbeam are driving that state into the ground.
You just hope Kalifornians and New Yawkers don't spread their politics to where they migrate to - they've jacked up south Florida, Colorado and WA state by doing just that.