How are people losing 20kg in 3 months?

Genuine question like I’m fascinated cause even if I was to consume 500 calories below my BMR (BMR is 2000, so 1500 in this instance) and factoring in daily exercise (usually 20k steps, OR 10k steps + 15km cycle) most calculators put my TDDE at ~3000 calories. 3lbs per week, 36lbs (16KG).

I’m honestly really curious, am I missing something? How much exercise are these people doing?

Btw I’m not advocating for weight loss that quick, I’m just curious how its possible.

Also, these guys aren’t like massively overweight either, they’re usually around 5’10-6’0, dropping from 220-180lbs or 100-80kg