I have a little bit of that happening (nowhere NEAR as bad as you have) where the tire of my truck rests in my driveway. I am also in Nebraska. I have been told ( by concrete contractor friends) that there are numerous reasons for this happening and they are on a case by case basis. Mine was because of lack of compaction over buried utilities under my drive. Most concrete contractors I have seen here don't even bother with compaction, they form and pour.
