You are swearing an oath to the Office of the King, not Charles Windsor. 

When the King is delinquent of his duties, it is the responsibility of the self governing people to uphold the Common Law of England principles for the benefit of the people.

The Constitution 1901 Preamble.

Correct me if I’m wrong but a Steward is responsible for the protection of the systems that keep the oblivious population safe, and because the Office of the King is sworn to serve and protect, we are just holding the fort.

We are effectively the Commonwealth Public Officers in waiting.