Yeah no shit the two characters who lost their beloved mothers, were abused and ignored by the rest of their family, and love playing the piano bonded. Why are people surprised by this romance?
They both had similar lives, it's just that she, being a powerless and incapable princess, chose to donate what little advantages she had to the poor. And he, a powerless yet capable prince, chose to rise up, seeking revenge for his mother and sister, wreaking havoc on the corrupt nobles while also taking pity on the weak.