Is favoritism normal for step-parents?

Is favoritism normal for step-parents?
I've been lived with my stepmom and two step-sisters for years. My stepmother used to favor her own daughters and she wouldn't care about me. My stepsisters had a lot of clothes, I had a few. They used to go to private school by bus, I went to public school on foot. They used to get pocket money from my stepmother every day, I didn't. They had their own room, I didn't have. In the so-called work section of the house, they would only clean their room and I would clean the whole house. My stepmom used to call her daughters 'baby, honey', and she called me just 'you'. Shortly, my step-sisters were like royalty at home and I was like the lower class. Do you think this favoritism is an instinct?
Is favoritism normal for step-parents?
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