In General Relativity. Gravity is caused by curvature of spacetime. In MWI and Bohmian Mechanics.. the position observable and position preferred basis is chosen. There must be a non-zero energy or some kind of dynamics that would lock the particular Hilbert space vectors into those special bases. What is this dynamics caused akin to gravity caused by the curvature of spacetime or akin to the non-zero value of the Higgs Field in the vacuum. You can't just say the position is chosen as the preferred basis in Bohmian Mechanics without any consequence or dynamics.