[DTV]

England has a few local radio stations, but Scotland/Wales/NI have much larger BBC organisations with a broader range of output. English regional TV production is largely non existent outside of news. NI gets a bit of both, as there's Radio Ulster and Radio Foyle

Sure, but there are various significant political and cultural reasons for that. With maybe a few exceptions, that isn't true for the patchwork of areas with very disparate population sizes that make up the BBC Local Radio network. Beyond petty rivalries, there isn't really much sociopolitical distinction between a lot of neighbouring Local Radio areas, creating arguably unnecessary duplication (even with increased simulcasting). 

While you might be sacrificing a degree of localness, a Regional Radio map that largely corresponds to the TV region map would not be losing much in terms of broader functionality - allowing for fewer, but better resourced stations with an overall lower pricetag. It would also allow for a noteworthy reduction in the BBC's property portfolio, a significant non-content related cost.