DAB is only useful for big stations.
The cost of putting a station onto DAB is prohibitive for all except the big players.
I have actually investigated DAB carriage (where I live) for a small radio station, the economics make absolutely no sense whatsoever.
Radio is all about putting bums on seats and then selling this audience to advertisers.
Going on DAB isn't about simply pushing a transport stream into a transmitter on a hill a few kilometres from your studio - no, you have to back-haul it to somewhere hundreds of miles, then you're at the mercy of the franchise holder's pricing model. If you're lucky you'd get 64kbps in mono on their mux.