Europe is bigger, Europe decides the rules for its airspace. Israel, as an outsider is seeking to renogotiate the deal - why on earth would Europe agree to that? Europe is doing a favour to Israel by letting it sign in the first place. It's like asking your neighbour to borrow their lawn mower - then demanding that they go out and buy a better one first.
from the article: EU officials warn Israel 'Open Skies' pact may be canceled