I can’t say a whole lot to the Pirate Faction ships, but I’d imagine this was intentional because transporting a cruiser hull or a battleship hull is a lot harder than a BPC. It makes it worthwhile for those who want to do that. I’m willing to bet, outside of locals and prior to the industry change, no one bought the hull with their LP.
In the case of the Navy Faction ships, it makes sense that you don’t need all of the new materials as the Navy takes care of that for you. All you gotta do is turn in a chip, a T1 hull, LP and some ISK.
It’s all about the trade offs here. BPCs were dominant for a long time and now there are legitimate reasons to purchase the hull instead of the BPC, and then haul it out to where you need it.