Why are electric witches, plugs and sockets made of thermosetting plastics?

The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics.

For example, Bakelite is a thermosetting plastic which is a poor conductor of heat and electricity. It is used to make electrical switches and handles of utensils.

Hence, electric witches, plugs and sockets made of thermosetting plastics.