When a ship is disabled, but nearby vessels may be willing to assist, what is the point of the master contacting the owners?

The owners may be able to arrange cheaper towage services on a contractual basis (e. g. stipulating ordinary tariff, fixed lump sum or a daily rate) than any salvage assistance that the master could engage from nearby ships. The master would be exceeding his authority if he engaged a more expensive salvor without consulting the owners when there was enough time to do so.