Its a surprise twist that will come up later, the previous Royals set up the system to take power away from the other nobles and centralize it, but it backfired in a terrible way. Thus every house lesser than a Marquis has spoiled cunts as daughters and wives, while the upper ranks keep a tight leash on their women, to the point where they are prohibited from having Demi Human lovers.
The King also uses this to get as many concubines as he wants, since there is actually a deficit of male nobles.