Sigswald is such an egotistical idiot. If he was actually following proper noble etiquette he should marry a second wife from within the duchy to manage the internal affairs and increase the archducal family's mana. Him expecting other duchies to CHOOSE to form political ties with him, through marriage, when he can provide nothing is ridiculous, especially when they'll likely heavily descend the rankings in the near future. At most he should try to marry an archduke candidate from a middle duchy who he could pressure, not Dunkelfelger.