First of all , that makes sense thank you.
just to be clear, im not looking for the lazy way, im looking for an explanation that doesnt necessarily need numerical values that are hard to get (but i will try to get it from my college).
I was thinking along the line, that it happens in the allylic carbon first time because of stabilization by resonance (hence the lower dissociation).
now second time we still have resonance, my guess is that it is more stable now because of the electron withdrawing group so it is harder to do for sure, anything can happen with enough energy id guess. but in theory wise, using NBS and a lot of energy, can it happen twice ? what if they put cyclohexene ---> (Excess NBS/High energy), how many times can it happen? is it anywhere in the books?