So much selfish greed. The kings greed for power ruined his relationships, the queen's greed for the king's heart caused her to become bitter and brutal towards the human queen and ultimately ruined her children's lives (causing her first son's nervous suspicious about having no one he can trust, and her second son's self sacrificing ways to promote his brother), and the goblin queen's greed for revenge on those who wronged her rather than trying to escape and follow a different better life. It all ended up harming the ones most important to them, their children, their loved ones, the generations to come.
And you can argue the 1st queen just wanted love, but she knew by marrying a king who was born during the next goblin bride's cycle she would have to compete and share eventually. She shouldn't have let her jealousy cause her to beat and abuse the other queen who was obviously unloved.