The thing is, all the other systems are connected to Jita like limbs are to main body. I think right now people will remove stuff from the disconected market hubs and move to Jita to trade because its more convenient to get everything there. Its like all the limbs where blood doesnt circulate have to be removed.
And if Jita will be invaded, it will be like CCP headshoting the game. Then it wil only rot in grave, slowly. Some ugly creatures may feast on it, but nothing more.