> Maybe they didn’t use the best grout and that’s wearing away faster than the surrounding concrete.

IIRC this is one of the disadvantages of concrete (as opposed to asphalt) road surfaces: it's very hard to repair them in ways that don't degrade over time.

edit: You can tell this road is "real" concrete because of the visible seams between each slab. For an ideal repair, they would have had to replace every affected slab of concrete, which is...all of them along this stretch.

You don't see these concrete road surfaces much near where I live (in Boston), particularly because such roads are much less safe when snow and ice are present.