Alas, users delegate this authority. They do not change defaults and let network admins decide where computers should point and what software will be used. The admins all point their computers to ICANN roots and ICANN roots are sometimes hardcoded into DNS software that admins insist on using.

Yet it is absoutely true, all it takes is changing some settings so that computers point elsewhere. ICANN derives its "authority" from voluntary behaviour of network admins.