I'm fairly certain it's because the Long Distance Vlocities will operate first on the Warrnambool and Albury lines, and then will be introduced to Bairnsdale and Swan Hill later after signalling and level crossing upgrades. Echuca, Ararat, Maryborough, Shepparton can all be operated by regular services.
I'm not sure that the assumption that VLocities will service all long distance lines is sound, at least in the medium term.
Sure, put them on the Class 2 Warrnambool and Albury lines, but you are wasting (and gaining zero) time operating them beyond Traralgon or Bendigo, to Bairnsdale and Swan Hill respectively, on Class 3 track.
Better off to construct a dedicated SG VLocity fleet for Albury or Wagga and convert the existing SG N-Set fleet back to BG for an enhanced service on the other lines. If my most recent experience is anything to go by, where an ordinary Up Bairnsdale service was booked out 2 days in advance (causing me to ditch the idea and drive instead of risking no seats available in Car D), more capacity is sorely needed for existing services.
I also find it a bit bemusing to consider the concept of replacing N-Sets when we still have H-sets running around!