The annual justification is that the royal family generates more in tourist revenue than they cost taxpayers. Their roles are largely ceremonial, and it can be argued that the constant photo ops and travel generate buzz for their product. Otherwise they don’t really do anything except generate expenses like a 5 million for travel including a helicopter to take Prince Charles 20 miles from his home in Gloucester to Highgrove. Dennis Kozlowski and other self-professed “ceremonial CEOs” could rack up 5 million for travel in a mere afternoon.
I doubt the the Royal Family would invoke the celebrity spokespeople defense if they were really in fear of losing their jobs. Are they worth the money? Would you be willing to pay the equivalent in taxes for a ceremonial head of state?