much has been made of the fact that a commoner is marrying royalty的正常语序是much of the fact that a commoner is marrying royalty has been made.
其中that a commoner is marrying royalty是the fact 的同位语从句；has been made是被动语态.
整个句子化简后是Much of the fact has been made.进一步化简就是Much has been made.
句子的大意是：在一个注重等级差别的国度,一个普通人嫁给一个王室成员这个事实是大量存在的.