Point of detail - their security has not been "pulled"
The current position is that they will received security based on the threat assessment at the time of each visit.
Harry is disputing that position, because he wants there to be full scale security for every visit, irrespective of the current threat assessment.
They have visited under the current arrangements, and may well continue to do so.
Official personal security teams are not available for hire. It's not the same as organisations defraying part of the costs of crowd control type policing (which is provided in line with needs assessment, not because an organisation wants it)