Because I've been involved in many a clean-up after squatters (almost inevitably well educated middle class dropouts in my personal experience), and that shit is not pretty. So someone is going to have to look after the inhabitants so it doesn't turn into a squat, run it, heat it, light it, clean it, etc etc. most of the many hundreds of existing staff - all of whom pay tax into the treasury too - would leave, and the many hotels, shops, restaurants etc would close because none of the hundreds and thousands of people who come to see the queen are going to come and look at a hostel.
So, you have to find a way to pay for it and top up the economy there too. As well as making sure that you replace it with a symbol to broadcast around the world to raise British tourism that is as effective as the royal family on the balcony.
I'm sure you've thought all this out as you're clearly v passionate on the subject (no sarcasm intended), so what do you propose?
I'm on the fence but swaying towards doing the works as part of our heritage and tourism, so intelligent arguments against it welcome...