This one again?

OK, the revenue from Crown Estates is paid to the Government. The Government pays the King about 30% of that income in the form of the Sovereign Grant, which is used for the various visits, tours and so forth that the Royals undertake on Government orders. If the Government were to tax Crown revenues, they would be taxing themselves!

Personal expenses are paid for out of the Royals' personal assets on which they pay tax. The amount is renegotiated from time to time because originally the Monarch and their famly were exempt. The Royal Family are honest and pay what they are asked to, with the result that they pay rather more tax, pro-rata, than the average tax-dodging non-dom or billionaire, and considerably more than the Churches, who are wealthier than all the rest put together and pay not a penny!

Finally, our Constitutional Monarchy, for all practical purposes, functions as a republic in which the role of President is non-political and purely ceremonial. The only difference is that in our case that role is hereditary rather than elected. To change that would either be purely cosmetic, pleasing only those who insist that every post from President to toilet cleaner be an elected one, causing rage among traditionalists and making not a jot of actual difference to anyone. Or we have a US style Republic and President Farage. One's not worth the effort, the other...?