There needs to be an understanding of the difference between 'wearing' and 'scratching.' Wearing is where the glazed surface is thinning and eventually actually work through. Scratching is damage to the surface from a harder substance that scratches the glaze. Heavy scratching can actually dull the surface of a glazed tile. It is damage to the surface, but it is not actually wearing through. Much like granite in a heavy traffic area will dull off from scratching, but is not worn.
The best way to avoid tiles becoming worn is to get good advice when selecting them. This way, tiles that are suited to the area can be chosen and that includes for reasons such as colour, ease of cleaning, durability, and resistance to wear.
The other way is to keep the floor clean and free from sand and abrasive dirt. This is especially important at doorways to the outside of a home or building. Abrasive grit is brought in under shoes and if there is a doormat, this grit is removed and left on the doormat. Even gravel (which can be equally as hard as granite) can be trapped under a shoe and then trodden onto the tiled surface.
Once the glaze on tiles has worn, it can't be rejuvenated in any way.
Likewise, damage by harsh scratching cannot be reversed.
Scratched tiles will continue to perform as a tile should. But, once a tile surface has worn through, and the protective glazed surface is gone, the tile will need to be replaced.