Take your imagination to the microscopic level and look at the edge. So at the edge you have a 12k finish and it is sharp but harsh feeling. Now when you look at the grain tips of the metal they are all lined up and sort of look like a saw blade. Some longer than others some farther apart. This is because the grain your at breaks some in half and some that are right next to each other. SO, now imagine you take that edge to a smooth stone with almost no difference or much less of a difference in size. The ends of those grains are going to line up closer together. It is now going to feel smoother because you have less of a saw blade effect.
Now there will be others who can explain it differently and even point you to electron microscopic pictures. And you also have other things to consider like blade thickness and the type of hollow in the face.

From my minds perspective that is a simple explanation you may be able to grasp.

The size of the grit and the shape of the bevel. Not to mention your style of handling the razor are all factors the give everybody a different perspective. Some like hollow some like wedge. I think most will agree the finer the grit the smoother the feel.