In the brane picture, the other three forces (electromagnetism and the weak and strong nuclear forces) are localized on the brane, but gravity has no such constraint and so much of its attractive power "leaks" into the bulk.
The other three forces (electromagnetism and the weak and strong nuclear forces) are localized on the brane. This is in the brane picture. Gravity has no such constraint. Gravity has so much of its attractive power "leaks" into the bulk.