From the grandparent link: When to replace your eye?

The tissue around the eye socket changes over time, and the eye can become scratched, even with careful maintenance.For these reasons you should replace your eye every three to five years, more often for children.

I can see that your question has already been answered, but I can confirm what it says. The cavity left after surgery changes over time, and the prosthesis, even if it is glass, eventually gets worn, leading to irritation. I presume that this is due to sand and grit in the air, which scratches the surface.

Additionally, you can have the ocularist recenter the eye prosthesis so that it better matches the orientation of your normal eye. Most eye prosthesis are approximate hollow quarter spheres resting on the eye musculature so that they can move in unison with the other eye.