You'd think her ass would get bigger, but as you can see, her projection has stayed the same while her thighs have gotten noticeably larger. A lot of these people act like their butt is big, when it's their hips that make up the bulk of their measurements.
Her "bigger butt" is mostly because of her thighs and hips. Unlike women like Thicksnoww whose butt you could literally see growing, and becoming greater in proportion to the rest of her body.