because he still couldn't forget her and was chasing her shadow (in my opinion) he finally could take someone who looks like her as a wife which he couldn't do before. he treated shuri like a possession that had to be perfect like the dead emperess
but from what we've read they weren't intimate or had a relationship. did he just want to posses someone that looked like the women he loved, I wonder
"There's two reasons; one is mainly because Shuri resembles Ludovika, second is because her resemblance to Ludovika would benefit Shuri on the politcal scene eventually – and he was right on that point, because the Duke of Nuremberg and the Emperor both showed a soft spot for Shuri in the novel/manhwa."
Cr. AdamantineW on Twitter
So basically, he did it to protect his family since the people with high and influential status would begin to like Shuli (since she resembles the former empress who they loved,) give Shuli a chance to achieve her dreams but also fulfill a weird sense of "I couldn't have my first love so I will take advantage of this opportunity to have a girl that looks like my first love and give her everything I couldn't do for Ludovika." I also kind of got that petty feeling that he wanted to show Shuli off the same way his friend, the Emperor had taken Ludovika to become Empress (since becoming royal means you become pretty established and wealthy.)
I was always curious since the beginning why the marquis chose shuri. Always assumed it would be something along the line that she would never pose a threat to his heirs. But after the recent chapters I’m more confused. Why would he marry her if she resembles the women he loved & is being tortured by her memory of her. Like why? For revenge against the king? Or peace? Still confused. Is he just mad/crazy?
But someone not in their right mind wouldn’t be able to train someone for 2 years to be the temporary head of the family. Need more. Just discovered this & binged it. Hopefully season 3 is coming