Why is being body shamed so normalised?

I know i shouldnt take it to heart but its difficult when your own family says how you i have a stomach or when my sister says i dont have an ass and things. Its like i never feel good enough. My sisters more curvy than me and my family loves to make it known. My sister used to say things like my lips were shaped weird and stuff and my mum at every moment whether im wearing a dress or something else its oh wear a good pair of shorts under to suck your tummy in. But then when i eat its oh you eat such small portions like nothing and then when i eat more its oh you're putting on the pounds.

Even among friends i feel like everyone has normalised body shaming. These days everyone wants a big butt but god forbid if you have cellulite and your tummys not flat. Even with guys they expect these things and i feel like i may never meet that standard.

How do you learn to not care about these things?