This is actually an incredibly false point. The royal family (if treated like anonymous land-owners) would cause a sudden and drastic drop in fundraising within the UK. Assuming their property wasn't seized having them retain their current station is actually a net positive to the British tax-payers - they lose far more potential income each year in free land leases and charitable donations (known collectively as the Crown Estate) to the state then they receive in benefits (known as the Sovereign Grant). This arrangement is financially detrimental to the royal family in terms of absolute value.