Why does body dysmorphia only exist in the present?

Like i look at past photos where i was the same bmi i am now and think i dont look that fat, but currently i think i look basically obese when is see myself in pictures and the mirror. When i was severly uw i thought i looked average, but now i can see i looked almost dead. In the future i will probably think i look alright when i look back, im so tires of this constant mind fuck.