Back in the day Ashley Cole was given dogs’ abuse for going from Arsenal to Chelsea, but there just seems to be no proper animosity now from fans towards former players. Cech, David Luiz, Giroud and now Havertz have all gone to the other side, but no one really seems to care and all those listed seem to still be well respected by their former club (apart from Havertz, who no one seems to care about either way).
Why has this rivalry died off? Arsenal and Tottenham players would never transfer to each other, nor Man United players to city or liverpool etc.
Cole was arguably the best LB in the world when he left, and Arsenal and Chelsea were direct title rivals. None of those other names were as important or left at a time when the rivalry meant as much.