No, it has nothing to do with licensing issues.
1) It's just because the tracks are randomly generated based on input criteria. We plug in some numbers and it generates a track with those numbers. That's it. We can't hand-pick specific details for every single solitary tidbit of track, and that's why we can't recreate real-world tracks. The best we can do is hope that a course happens to come out looking vaguely similar to one, and even then it's unlikely that the dimensions will be right, that the elevation change would be right, that the camber would be right, et cetera.
2) Forza Motorsport 3 had Sprint Cup cars, but they were blank rather than having liveries on them. Nevertheless, using the awesome livery editor players recreated many real-world and fictional NASCAR liveries and exchanged them publicly, and there were no licensing problems at all because these things were user-generated rather than generated directly by Turn 10. The same should work just as well for tracks created in Course Maker.