What has the family done for the country in the past 70+ years, beyond use of resources, horde their castles, and provide tabloid headlines?
The Windsors are very, very rich on their own. And the Queen and her husband set an example of how to behave in public. They are the ultimate greatest generation.
They're an industry. They are an enormous tourist draw, attracting millions of tourists (and tourists' money) from all over the world. They contribute enormously, and purposely, to the British economy. The companies and activities they support provide great numbers of jobs and pay considerable sums in taxes. Unless you go there and see it for yourself, you cannot comprehend the powerful effect they have on the British economy.