They’re not giving them more money, the sovereign grant doesn’t come from tax payer money. It is a % of the profits from the Crown Estate.
It’s also not their private money to use for personal spends. The increase is temporary because of increased profits and to be used to repair Buckingham Palace. After this year, it is going to go down
The Sovereign Grant is paid annually by HM Treasury at a value indexed as a percentage of the revenues from the Crown Estate and other revenues in the financial year two years earlier.[7] It is based on an index percentage that was initially set at 15%[8] and this is reviewed every five years by the Royal Trustees (the Prime Minister, the Chancellor of the Exchequer and the Keeper of the Privy Purse).
Since its inception, the Sovereign Grant has often risen each year at a rate higher than the rate of inflation. About a third of the grant is used to tackle the backlog in property maintenance at the royal palaces. Following the 2016 review of the percentage of the Crown Estate income used to calculate the grant, it was announced that a temporary increase in the Sovereign Grant would be used to fund a £369 million refurbishment of Buckingham Palace, subject to parliamentary approval.[10] The trustees recommended that the percentage should rise to 25% for the 10 years during which the work would take place, and that the grant should then be returned to 15% when building work is finished in 2027.
n January 2023 the Keeper of the Privy Purse, on behalf of the King, asked the government to reduce the percentage used to calculate the sovereign grant so that the total does not include the income from new offshore wind power leases, calculated to be worth around £1 billion annually to the Crown Estate. This request was said by the King to be due to his desire that the money could instead be used for the "wider public good".[15] In July 2023, due to the Crown Estate's sale of wind farm leases dramatically increasing the money going to the Treasury, the government announced that the grant would be 12% of the Crown Estate's net profits in the following year, down from 25%, while maintaining the same level of payment in pounds
In July 2024 it was announced that the annual profits from the Crown Estate had risen again due to the proceeds from offshore wind projects, resulting in an annual increase of £45 million to the Sovereign Grant for 2025–26.
The Keeper of the Privy Purse said the increase will be used to complete the renovation of Buckingham Palace, and that once this was accomplished: "a reduction in the absolute amount of the sovereign grant will be sought as part of the royal trustees review in 2026–27, through primary legislation".[17]