Why do we listen to our radio station(s) of choice? Because we know what they stand for and like what they primarily do.
The Capital brand is all about hit music and showbiz content and the average listener will tune in for exactly that, regardless of where the morning show comes from.
In fact, a better-resourced national breakfast show reaching millions of people is better for the brand as it attracts bigger guests. How does it make sense to get Dua Lipa into Leicester Square only for her to be heard in London and not by the 73% listening in other parts of the UK at that time?
For the likes of UKRD and Lincs FM Group, being authentically local is the core of their business in such a way that it's a reason to listen in itself. For others, it's more about sponsorship and promotions and to comply with Ofcom regulations.