While a wheel bearing must support its share of the vehicle’s weight, it must also maintain a perfect radial alignment with the axle. The instant it does not, the rotor pushes the caliper pistons into their bores and drags against the pads.
Even with drum brakes, a wheel bearing must maintain the concentricity of the drum with that of the brake shoes. If the axle moves, the brakes will drag and axle lubricant will leak past the seals onto the brake shoes. For more information read the article.