It was okay for Lizzo to be fat when she was still a nobody, only performing occasionally. But getting up and performing on a regular basis--and being expected to dance, and do all that shit in high heels? That woman's success has probably come with a lot of foot, knee, and back pain from trying to perform like one of the skinny girls. If she wants to keep performing like that, she really does need to lose weight.
And there's also the possibility she's had an obesity-related health scare, such as diabetes, that she's not forthcoming about.
Her music's not my thing, but I have nothing against her, and hope she succeeds in taking off the excess weight and sorting her shit out. It's too bad she's going to discover just how many of her fans only love her for her body size and shape, though.