why would she do that to me?!

does anyone know what causes people to rape other people? it confuses me! i mean im still trying to figure out why my own sister would rape me when i was 5 years old! Im not feeling any sypethy for myself by the way. i prob deserved it thou. im also wondering why my therapists and parents would just look the other way after i told them. its like they didnt even care. i told people i was close to (two people) and they just dont care..thats the point i noticed that nobody truely cared about me. thank you for letting me share. i just had to get that off my chest, cuz im going thru too much right now and im needing help