When the British government taxes Caribbean-heritage British citizens and sends part of that revenue to Caribbean governments as reparations, it is in effect telling those citizens that their contribution to British public finances is earmarked for a payment they may not want to a government they did not choose.
This would be unusual in principle for any British citizen. For Caribbean-heritage British citizens, it adds a specific indignity: the implication that their taxes flow back to the Caribbean because that is where their real obligations lie. It treats them as Caribbean people who happen to live in Britain rather than as British people, which is precisely the attitude that made the original discrimination against the Windrush Generation so wrong.