@Doomer @Serkket As someone else here mentioned, it's clearly not in Rovel or any of his relative's interest to take over as the new royal family. The nobles benefit from a royal family which have their own personal distractions or are easily lobbied. And putting aside his obsessions, the prince is clearly a capable person who can provides the country stable governance.
It might seem odd when you just think about it shallowly, but a royal family can't govern on it's own. There is no simple easy solution where the Vankreift family simply stages a coup. Assuming they take over, they need the cooperation of the other nobles to govern. Even before that, the country is not at war, not steeped in poverty or other problems. A takeover is not likely to be well-favored by even the citizenry, who from their perspective will just see a powerful family abusing their military power to enthrone themselves.
I'm just a little annoyed. Manga is often panned as being overly simplistic and shallow at times. Here you have an example (even if it's just one chapter and scene) where the writer is willing to tackle a deeper political angle on the story (and honestly, it's not that complicated). Even Ellen's declaration at the end, as showy as it is for manga's sake, highlights that she can say what she wants because she's tied the Prince's hands through her maneuvering. It's great. But the comments here remind me that manga, for those same traits above that it's often criticized for, has also attracted readers who look at it equally simplistically and shallowly.