Dxj of Habitat Quality

Hello,When calculating the degree of degradation Dxj , the formula (4-3) normalizes the weights, but does not normalize the threat of all grid cell y to the grid cell x, so I think the Dxj may be greater than 1. But in the final output, the degree of degradation in the degradation score map is less than 1.
So I hope someone can explain this question to me.
Thank you for the attempt.