Broadcast power of DAB+ compared to FM broadcast
The problem, best I can see with UK DAB and DAB+ broadcasts is that there are too many small transmitters. Based on this website that monitors transmitters.
Largest transmitters with DAB+ are running at 10kW. Largest FM transmitters can go up to 100kW (I don't think they go any higher for technical reasons in Europe).
Bandwidth in Mhz for DAB+ seems to be limited to 1.5Mhz and that is not a lot of bandwidth for high quality music in digital format. FM has maximum bandwidth of 270kHz with RDS.
https://www.ukwtv.de/cms/grossbritannien-dab.html (DAB information)
https://www.ukwtv.de/cms/sender-tabelle/sender-tabelle-ukw.html (The FM transmitter table for UK has been removed)
https://en.wikipedia.org/wiki/FM_broadcasting (FM Radio technical stuff)
Time of FM radio broadcast is probably just ending, like analogue phone in homes and other old technology. Its going to take a while to happen in all countries.