There are still factions that use the Border World line that aren't Outcast or have no affiliation with them. Like the Bundies. The Border World line is still available to use by Outcasts, so they don't need an entire full ship line. Outcasts don't own exclusive rights to the BW ship line either, they likely got it from someone else.
When I made the Cutlass for a new BW Bomber, the idea was that the Falcata was being decomissioned (Unlike the rest of the BW series, the Falcata was produced originally by Outcasts) in favour of the new Curtana model, Eppys one. Because this technology had a very distinct Outcast flair about it, concerned parties in the Border Worlds developed the Cutlass to replace the Falcata once it was decomissioned.
Though, right now it seems like the Cutlass will likely just replace the Falcata.