It's not just Korea. Are you kidding me. If you're just slightly overweight in my country, people will openly tell you you're fat and kids make fun of you. In the US, even though 30% of the population is obese, fat people still get bullied. It's more obvious if you look at like YouTube comments, what people truly think. What you're expected to look like.
But I agree it's disappointing she just lost her weight immediately, that was a big eye roll moment.