Well, the reason that not all electrons can jump from nucleus to nucleus has to do with one thing: resistance.

Resistance is how easy or difficult it is for electrons to move through a substance. The lower the resistance the easier it is to move, and the easier current can flow.

Let's see this in a few different materials. Our friends will race through a tube of air (low resistance), a tube of sticky goo (medium resistance), and a tube of solid ice (high resistance).