"supporting the Taliban insurgency in Afghanistan". What ISI, like most similar organizations in the world support, is what makes money for them and what gives them power and a feeling of control over what happens in the country and the world.
If Taliban didn't exist, military business and mass control means such an organization, called anything you like, would need to be created. It make look like "Taliban is been supported", but it is not. Taliban has been created and is "being used", to support official national and international military business, or, to give it the correct name, the Arms Trade.