Why don't birds get electrocuted when they land on an electric wire?

The current has to pass through them. If they were also touching a metal frame or similar they would incinerate. BTW still love your avatar.

they are fake   

They occasionally do and it often arcs. 

The copper in electrical wires is a great conductor. Birds are not good conductors. That's one reason they don't get shocked when they sit on electrical wires. The energy bypasses the birds and keeps flowing along the wire instead.

As long as they don't touch anything grounded, like a pole, or two wires at the same time, the electricity has nowhere to go.  Birds have been electrocuted by landing on one wire and then touching another wire with a wing.  And occasionally one will hop over and make contact with a bird sitting on the pole or will touch the pole while still touching the wire.  

For one thing those wires are insolated. Secondly each wire on the electric lines in only one leg of the circuit. It takes two legs of a circuit to electrocute. The wires for each leg are too far apart for then to straddle unless they are very big bird and I don't even think Big Bird could do it.

They need to touch more than one wire to get electrocuted.