Why upper hole is bigger and upper pin is longer?

Wall socket and Plug

When we plug in an applience to the socket, if there is a short circuit fault in the circuit in the appliance, it will make a bigger current. When the earth pin connects to the socket, this fault current is grounded. Since the earth pin is more thicker (pin hole is more bigger), it can carry more current and then current will be grounded effectively.

Since the earth pin is longer, this will connect to the socket first, before live and neutral pins are connected. Then, if there is a fault current in the circuit of the appliance, it will be grounded first making all are safe, before entering more current through the live pin to the circuit.

So, here is the reason. Hope you got a basic idea for ‘why’.