The franchise model is 30 years old, going back to privatisation. Since then there has only been one significant attempt to rearrange the franchise boundaries, about 10 years after privatisation.
The railway is now stuck with pieces of franchise jigsaw puzzle that are unfit for purpose because of the subsequent changes to the UK economy generally and transport use in particular. The strains this poses are exemplified by the long running saga of the East Coast Timetable revision. Another example is the capacity constraints at Ely, where 4 different TOCs defend their existing rights instead of devising a timetable fit for now, not fit for 20-30 years ago.
The franchise model is now an obstacle that is hindering the railway's ability to adapt to change. The Great British Railways model will facilitate the reallocation of resources to where they are most needed in a way that can't be done now because those resources are ringfenced in franchise silos.
I went through lots of reorganisations in my working career, most of them more trouble than they were worth, but this is a reorganisation that I think is necessary.