In order for SureFire to pass on the cost-savings of getting DL123A batteries OEM from Duracell, SureFire had to sell the DL123A's inside a product. SureFire threw together (and patented) their 12B as a low cost 'illumination tool' that was the most cost-effective means of buying CR123A's possible.
When SureFire decided that DL123A batteries were still too expensive and it need to act to ensure customers got a better deal; SureFire created their own brand label of CR123A's and purchased sufficient quantities to get the lowest possible price. There was no longer a need for the 12B so it was discontinued.
The fact that the 12B came with a bulb is only because it had to.