What can cause this wear

[bwake]

This is normal wear for a steer tire. Those in the tire business refer to this as erosion or river wear. There is no corrective action for this type of wear and usually starts to show up during the later life of a tire. I've attached a guide to help diagnose tire issues and this one is at the top of the page to the far right. Cheaper tires show this earlier but it happens to all tires. Based on the rest of the tire, I'd guess that the alignment and balance are all in good shape.

https://www.michelinb2b.com/wps/b2bconte..._Steer.pdf