The starch molecules interact with each other in a different way than water does. They are not like tiny marbles rubbing around each other, but like sticks or strands of straw.

With low shear force, they are not compressed enough to turn into a solid. They can still slip by each other easily. The water may provide the "grease" that keeps them from sticking in this state.

With higher shear forces, they lock into one another and form a solid.