I mostly just do it for completions sake. Sometimes you need to be a horrible person to see everything a game has to offer. Anybody who's defeated Sans knows what I mean.
It kinda sucks that you can't get to Kive's storyline any other way but romancing Margaritta. In fact, Margaritta may be the least interesting character for me. She's simply too perfect at being her character's archetype, and gets fully revealed in like 2 dialogues: she is a hard worker, believes in destiny, very kind and loving, that's it. No cons at all. So if you want to see a story deeper than "a daily life with an ideal cowgirl girlfirend", you have to cheat on her.
It feels like those cheap anime lovestories: "Omg, I love A-kun, I want to be with him for the rest of my life, it is our destiny. Oh no, B-chan seems to be intersted in him too, even though she knows that he's already mine. But B-chan is my old friend, how could she do this to me? Omg, she actually was just testing A-kun because she was worried about me, I am so thankfull to her! Nothing will stop our love now! Oh no! Another old friend - C-chan is also interested in my A-kun! How would that turn out?!".
It's totally fine if you enjoy them of course, yet these saccharine lovestories are just not for me. I guess I'm more into drama with character revealance, like Maryen and Madea, or a simple romance, like Sheina and Eliette.