Hmm … Many things can be a currency.
The old families have forgotten themselves. Spent too long huffing their own farts, in a sense. Believing themselves above the menial taskings of life, they have lost their ability to live and to relate.
As such, they have lost their power. By their own logic. The king cannot order back the tide and no sailor would do so in earnest.
In short… They have become caught in their own illusion.