Hmm, I was always under the assumption that it was the opposite... millennials were more likely to uproot to go to job hubs or moving from the midwest to "trendy" cities... well, I moved 7 miles down the road from where I grew up so I dunno. A number of my friends have left, due to high living costs for my LIer friends and a dead job market for my college friends upstate.
I'm not too crazy about LI/NY metro but it's home, I've got family and a good job here, and can't really think of too many places I'd rather be (maybe Seattle, DC, or San Diego).