I understand the diagram — it is pointing out a straightforward consequence of the earth being an ellipsoid — not a sphere — meaning things on the surface that are “vertical” do not point exactly away from the center of the earth, except at the poles, etc. Not a consequence of gravity or the density of the earth, just the shape. Thanks for the diagrams.
The ellipsoidal shape is the shape that would be assumed by a rotating liquid held together by gravity and bulging in the middle due to centrifugal (not centripetal) force. The surface gravity arises from the shape - a sphere surrounded by the toroidal bulge. The gravity due to the (homogeneous) sphere would be in the direction of the center of the sphere. The gravity due to the toroid would point towards the part of the toroid that happened to be closer, it would tilt the gravity vector towards the equator, unless you were at the poles or equator, where tilting towards the equator is no tilt at all.
As you get further from the center of the earth, the differences in the tugs from the left and right side become smaller relative to the total gravitational vector, and the field looks more spherical, i.e., the gravity vector points more nearly towards the center of the earth, so the higher you go, the more nearly gravity points towards the center.