So, that CNBC article summarizes an article in WSJ that cites 27,000 people leaving some of the largest cities in the US. The problem is that the changes in each city are actually much smaller than the margin of error for the data that WSJ uses (I think it was ACS 5-year estimates).
Edit: 27k is approximately 0.25% of all 25-34 year olds living in cities with pops over 500k (which is what WSJ reported on). Not an exodus at all and it's really a bit of a nonsense narrative that WSJ has been pushing hard.
This post goes into more detail on why that narrative is most likely noise: http://cityobservatory.org/no-youth_exodus_signal-noise/
Edit: 27k is approximately 0.25% of all 25-34 year olds living in cities with pops over 500k (which is what WSJ reported on). Not an exodus at all and it's really a bit of a nonsense narrative that WSJ has been pushing hard.