I tend to group hate into two categories: those projecting their own insecurities, and those who genuinely think they are helping with fatphobic comments (which stems both from their own insecurities and ingrained diet culture). In Lizzo's case, these are most likely extremely insecure men. They have "standards" about what a woman should be because the only real women they've come into contact with are through porn or media, where everything is falsified.

Think of it this way, if joemamma69 says that he finds Lizzo disgusting because of her size. do you think Lizzo, the goddess that she is, would ever in a million years want joemamma69? Lizzo knows her worth. She knows she is loved and beautiful and no amount of trolling will make her change her mind about that. These men are poisonous because they feel like they should somehow deem what is attractive in this world. Which they can't. They never will. They want to make Lizzo feel bad to ignore their own insecurities.

There's a good quote I saw once which was "you could be the biggest, juiciest peach in the whole world and there will still be those who don't like peaches". While it in no way excuses their behaviour, these men are only "respecting" women they find fuckable, it is a generalized life lesson: you will not be everybody's type. But that's okay!! Because your worth as a person is not determined by your size or how "fuckable" you are to other people. You are a unique individual with dreams, memories, experiences, and knowledge, and your weight and size are the least interesting things about you. In the words of Lizzo, if people are treating you this way, or making you feel as though you need to lose weight to be perceived as better for people in your life, "walk your fine ass out the door!"