I've never seen a highway with a hill so steep that your visibility is less than stopping distance. There's an exception to every rule, but I'd wager that it is at most exceedingly rare. It's definitely not regular.

Texas has u-turns at basically every highway intersection, with exceptions like this photo. The u-turns bypass the stop sign/lights so that it's just a yield. I'm not sure if any other states do that at the same frequency. With that design, it's probably easier to just raise the highway since it's a straight road rather than raise an intersection. I'm sure it also depends on which road was there first.

The huge access roads also typically stop at intersections, unlike in this photo. In order to support that and have the smaller road use an overpass, the access roads would either need to be built much further away from the highway or curve out and in at every intersection in order to reduce the grade of the overpass's slope. The overpass would need to be longer too since it's crossing more lanes.

If the smaller road goes over the highway, it's pretty common that the highway actually goes down so that the smaller road needs to be raised less.

I'm sure there are plenty of other positives and negatives, but I'm not a structural engineer. I'm just pointing out that it's not an arbitrary decision and it comes with some benefits like robust access roads and u-turns.