Weight which is why the rows and stands are made of cheap aluminum. Any additions would have to be light weight and cosmetic. Fortunately the arid climate doesn’t cause decay in the structure to the degree we saw at aloha stadium.
The only way to do major renovations is to stabilize the soil with stone columns and pile rods. It can be done but it is a significant cost.
The better alternative is to tear down Provo High and build a new stadium there with a tunnel to the indoor practice facility and student athlete building.