electrostatics - What moves the charges between capacitors?

Suppose I charged two capacitors to charges Q1 and Q2. By charging a capacitor to charge +Q , I mean that one plate acquires a net charge +Q and another plate acquires a net charge -Q.The capacitors were isolated when they were charged.

Now consider the two cases:-

1)When only one plate of each capacitor is connected through wire . For this case, I have read that charges will not flow between the connected plates but I want to know why ?. I have read explanations like the two plates will come to the same potential (but why?). I haven't found the reasoning for it .

2)When both the plates of one capacitor are connected to both the plates of another (as shown below) through wires. For this case I have read that charges will redistribute .

I want to know what force causes the electrons to move and what is the fundamental physical difference between these two cases .I want to know how do the two capacitors know whether both their plates are connected or not .