Where do you live? Mars?
Unless you live in a part of the country that is more than 40 miles from a major population centre, extremely hilly or mountainous, or the former and never travel out of your hamlet then either:
1) Your car radio or antenna are faulty, or;
2) You've not had the multiplex learning feature explained to you; or;
2) You are not being entirely honest!
I've traveled most of the country (yes, up North as well) and listened to both National and Regional DAB multiplexes without much issue. I am happy to defend FM to the hilt - it works and it's great, however I get fed up with all the DAB bashing - it simply isn't that bad any more.
One of the bigger problems with DAB is that it does need to frequently re-learn what's available to it, and some of the older radios don't perform that function automatically. This, to my mind, is the biggest oversight with DAB; along with regional stations not linking their multiplex handover information.