What killed it?
Texas Instrument.
Texas instrument to throw in the towel.
Arduino stopped making the new developement board.
The first board were only changes of Wiring boards, as IDE which is a fork of Wiring.
After avr :
Zero : the work was done by Atmel
Galileo, Edison : the work was done by Intel
Arduino LLC is not able to do new developement without the "active" help of micro-controller's manufacturer.
It seems that Texas Instruments was no longer interested in the Arduino world especially since he is cut in two.