Two thoughts.
1. What do people think that the Virgin brand brings to any enterprise in 2019? To me it's redolent of a generation ago. No-one would choose it as a brand name now. As I see it, Branson's involvement with the businesses is limited to collecting the license fees for using the name.
2. Clearly Virgin is interested the feed into its longhaul network at LHR. I would suggest that the feed into MAN is less important because, with the exception of the periphery (NQY, ABZ, INV) access by road, coach or train is the norm.
AndThe strength and weakness of the current Flybe network is that it is trying to fill two roles. From Scotland in particular, but also from NQY, it serves business markets for journeys which in many cases cannot be carried out as a day trip in any other way. The classic example of this would be EDI to SOU. And that journey is sufficiently awkward that it will also attract non-business traffic. However business traffic falls away around holiday periods, and Flybe has sustained its SOU base by using these UK services to feed into a network of flights serving secondary airports, particularly in France.
This tapping in to different markets is a strength, but it seems to have resulted in a lack of focus. And as Ryanair serve more destinations directly, Flybe's summer holiday business must suffer.
This domestic network is important, and can be substantial (EZY fly several times a day between EDI and BRS), but it is of no interest to Virgin.