its because aluminum intercooler pipes are realy good at getting rid of heat, i know they are also good at conducting heat. but they let the heat rise alot quicker than conducting it. so insulating it could help but the heat from the compressor discharge 55deg to as high as 85 deg going through the piping wont be able to transfer through the piping and in to the engine bay.
i dont work with aluminum often, lagging(insulation) is generaly for metals or plastics that conduct hot or cold air and dissipate them too.
its a win and lose situation me thinks