Can someone explain the correlation between weighted blanket weight and body weight?

I was looking at various web sites for weighted blankets for the winter. Interestingly, they seem to be sold with some connection to body weight -

250 lb. person – 25 lb. blanket
200 lb. – 20 lb. blanket
and so on, roughly the blanket should weigh approximately 10% of the person’s weight.

But nothing explains WHY that 10% is being recommended.

What’s the theory?