Why do my parents want me to be the butler of the family, whilst my stepsister does no chores the only chore she's ever done is cook 1 per month?

I do all the cleaning & heavy lifting jobs. The only job I don't do consistently is cook per day that's it. Nor do I understand why she always got the free pass from step mum to not do anything baffling?
Why do my parents want me to be the butler of the family, whilst my stepsister does no chores the only chore she's ever done is cook 1 per month?
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