I do not believe I am a part of said "hotness", nor do I completely understand it. However, I believe that for a significant portion the attraction is related to:
-Number of young single people engaged in the arts and creative industries
-Reputation as a "Frontier" neighborhood
-Proximity to bars and restraurants filled with single, young people in creative industries.
-availability of apartments in which the entire building will be similar in make-up: young, creative, single.
-known availability of good quality marijuana via delivery.
-ease of renting apartments, in light of not having a long credit history or a salaried position. (i.e. Mom will be accepted as a guarantor): http://jmrealty.org/pdfs/guarantor.pdf
Note, proximity to midtown does not seems to be weighted as highly as the above. Crime is seen as annoying, but falling.
In short: A lot of people want to live here, and are willing and able to pay a lot of money to do so.
For better or worse, the change on Nostrand is going to make the change on Franklin look minor.