I suspect that they want them to be special in some way kind of like each pirate ship is now. The Mach was known to be a great sig tanker, the Nightmare was just plain incredible as a slightly unstable Sh Tank Energy Turret beast, and etc.
Trying to find such niches for new pirate BCs without just releasing a few could be challenging; and frankly, anything they could do would probably be trolled to death for being “lackluster” by some in the player base. Sometimes the players can be their own worst enemy when it comes to such things.