@Raebit There is absolutely no fucking reason. Author has no clue how to create a backstory, so he went with the typical "hurr durr I hate my child just because."
It was literally said she was always being compared to her sister, and she couldn't meet their expectations. She was gloomy and quiet, while her sister was cheerful and social.
But it seems like she was abandoned from start then afterward they start being compared.. (the vibe, not actual fact)
Her sister like a young lady and her being servant vibe.
Do MC at first treated the same as her twin before? now I'm kinda curious.
Since MC feel inferior very much.
2 years late BUT:
Without knowing the future plot the abandonment could be a case of a culture where the 2nd twin is seen has demonic, either that or simply lack of resources/willpower so they decide to pamper one and neglect the other.
Future chapters'll probably prove me wrong.
there's a lack of composition as to why our MC has been thrown out. i hope we'll receive that backstory some day. i feel it's likely gonna be a cliché, but well, cute story, cute loli, so who cares. :3