Is it mostly aesthetic damage?

I find it hard to believe NASA didn’t think of everything.

There is a risk that partial splits of the wheel could damage the rover's wiring, but they have a cunning plan to rip the affected part off before it can cause damage. The stongest part of the wheel would survive (the central rim) they could drive on that for years

They did think of everything they and everyone else knew at the time, but Mars rocks were more embedded in this part of Mars compared to those seen before. It was designed to last 2 Earth years, it's been running for 14, so all is good. It'll run for many more years :)

I recall when the first holes appeared in these wheels, all the doomsayers were telling the world its be unable to drive etc etc... that was a decade ago, and it is still roving, and climbing a mountain :)

NASA didn't think the surface of Mars where they landed the rover would be so hard and rocky, basically.

They need all-purpose wheels that can traverse sand/gravel/bedrock, and to go through sand they need to have a large surface area to distribute the weight and stop it from getting stuck.

But when you drive over bedrock sprinkled with the occasional bit of gravel, the point contact pressure of the gravel is high enough to break through the parts of the wheel designed to sit on sand, in the same kind of way that you treading on a little bit of Lego hurts, you're putting your whole body weight on a very small object.

Then you add in the fact that they need to be as light as possible, and also need to withstand -60 to -80 degree C temperatures and a lot of UV (so rubber/nylon/plastic wheels are out) and you end up with the compromise wheel that they have that can be easily damaged.