Another reason DAB has been slow to catch on in Germany: Listeners remain satisfied with the performance of analog FM. RDS, with its "alternate frequency" automatic retuning function is running on nearly all of the stations, and many factory-installed car radios include this feature. You can tune in a regional station in Munich and drive all day through Bavaria without having to touch the dial. The public networks maintain excellent main transmitter sites, as well as translators to provide fill-in service to small communities, and their philosophy towards audio processing generally favors quality over quantity.
I would guess the Germans decided to concentrate on internet radio because, as a software-defined system, it offers an easy upgrade path.
Although Eureka-147 DAB offers the advantage of single frequency networks, weak error correction and mediocre audio quality of its "hard wired" MPEG-1 Layer-2 codec leave much to be desired. An updated standard (DAB+), which uses the AAC+ codec, has recently been introduced in Europe, but it's not backwards compatible with existing receivers.