The US is incredibly "bandwidth challenged" due to decades of poor frequency management of the nations airwaves by the FCC. We have some frequencies that are highly managed and tightly coupled for maximum use being auctioned for billions while other equivalent segments sit stagnant for uses that should have been put out to pasture 30 years ago. This is why almost every new technology (WiFi, Bluetooth, cordless phones, etc) is relegated to the mostly unregulated 2.4Mhz ISM band. Read about it here:
Why Everything Wireless Is 2.4 GHz | WIRED
Thus, DAB makes technical sense (a lot more channels can fit into the same frequency range) but with the various lobbies and ongoing political strife in Washington, its hard to see FM radio changing in the US anytime soon.