
That’s because Castiel killed unimportant side characters with basically no names and no emotional attachments. The prince killed the main character who we had to watch suffer and work hard only to suffer some more and then die horribly. The difference is the portrayal and that is huge. Just because Caitel is a horrible person he really isn’t portrayed as such in any of the chapters visually. He’s described that way and everyone acknowledges it. The prince however is shown as being terrible to Tia but is generally described as being well loved regardless. So there’s the feeling of injustice there as well.

Plus, Caitel has never been horrible to Ria, even though at first he was only tolerating her after deciding not to kill her, he's never mistreated her and came to cherish her pretty quickly despite him being oblivious to it. No matter how horrible of a person Caitel is to the rest of the world, he loves and cherishes Ria and Ria can't help loving her dad back because he raised her with love. Since the story is told from her point of view, we can't help but have a soft spot for Caitel as well. Same with Tia's prince. It doesn't matter if it was in Tia's past life, we saw how horrible and despicable he was to her. Going back in time doesn't make her pain and suffering go away. She still went through all of that and we as witnesses of it can't like the prince that easily. Stories are written for us to sympathize with the main character, not with some random no-names

Also I would like to add to my previous statement:
When a dying woman (that you liked/crushed on) BEGS you to take care of her 6 year old daughter it does not include the following:
Neglect
Emotional and verbal abuse
Being treated like a villainess
Burdened with extreme workloads
Torment
Rape / physical abuse
Tossed aside
Cause a miscarriage (through the stress of all the above)
Murder her father
Execute her after making her kiss your feet to save said father
And this all happened because she was what? Cold? Because she didn’t feel like could express her feelings because of her position that everyone expected her to be perfect?? Because of that she was somehow not human to him so he hated her because?? Why??? When all she did was love him and do her best to be what was best for the country as an empress should be?? But some dumb hoe pops out from the sky and all her years of effort and hard work are thrown out the window and chopped up by a guilotine.
Thinking about it all over again is making me sooo angry I can’t even.
There is something I don't understand. Why do people hate the prince from "The abandoned Empress" but like Caitel?
From my point of view it should be the opposite. I mean, Caitel killed I don't even know how many babies or people in general, while the prince made life difficult for Tia and killed her but in his previous life. In this life he is "almost" sweet and caring for Tia, he doesn't even know he has ever been evil, while Caitel knows and has is bloody past on his shoulders. Why do we hate one and love the other? I don't think it's right