Surely playing music doesn’t require that you you connect your phone to your car?
Pretty much all cars also support bluetooth, USB sticks, and some still have Aux in. Some support various internet radio/music (spotify etc). Most cars support Android Auto/Carplay, wired and wireless, giving you access to anything your phone supports.
According to https://www.acea.auto/figure/average-age-of-eu-vehicle-fleet..., the average age of a European car is over 12 years. It'll take another seven years for your average European car to have DAB+ support, let alone all cars.
In theory any old car can support DAB+ but car accessory manufacturers like to as ridiculous amount of money for car radios, so I doubt this change will occur faster than the car replacement rate.
DAB+ has been a complete failure so far. Its reception issues are even worse than FM and of the few people I know that have even heard of it, nobody cares. The benefactors of the DAB+ transition aren't the people listening tk the radio, but the radio stations fighting for frequency space.
(norway and switzerland are both mountainous countries, which meant the same FM station had to maintain several different transmitters on numerous frequencies — if you're in a country flat enough to serve with vanilla sugar and hagelslag, might that have something to do with our divergent experiences?)
Furthermore, DAB transmits on an even higher frequency than FM, so mountainous areas will need more transmitters than with plain FM, not less. Sure, the combined digital streams DAB provides are used to reduce the amount of transmitter installations, but that also could've happened with FM.
DAB is far from a failure. It'll eventually replace FM by mandate, because there's an incentive for governments to let more radio stations pay for broadcasting licenses. However, it's also far from a success at the moment. Access to streaming services such a Spotify or the internet broadcasts of the radio stations themselves has probably eased the transition as well.
Why would I listen to what the station programmers decide (and possibly riddled with ads) when I can configure my phone to play whatever I want when I want?