Probably a big chunk of these tried ACC a few times, found that ACC sucks unless you're on perfectly clean empty highway, and said "screw it I'll drive it myself".
I've played with it a little bit. Seems useful in principle. But a lot of roads I tend to be on--even highways--have a fair bit of traffic and speed limits that change on a pretty regular basis. Hasn't been as useful as I expected it to be.
