You can drive across the entire United States in as little as three days, if you do it right, and that's averaging two or three drivers and minimal stopping times. But that's in a small car, with nothing but road ahead of you.
Car transporters can't say that. Sure, they drive across the country all right, but it usually takes them anywhere from 10 to 14 days, on average. But why? The main reason is that they can only drive so far and so fast; they can only drive 11 hours maximum during any given day, and of those 11 hours they can only drive 8 hours consecutively before being forced to stop. That's not easy for carriers to do, but they do it because it's the law.
And that's why auto shipping takes so long. The worst part is there's nothing you can do about it, either - all those restrictions come from the federal level.