Or they're hoping it finally becomes a marquee title. Just because they push them as one doesn't mean they are, breh.
Like I said, they may not be a complete money sink but they don't bring in tons of revenue. Sony will keep making them, unless one completely flops, until the series catches on like they want. What other FPS exclusives do they got. Resistance 3 was piff but that shit flopped hard and murdered the series. Sony has nothing but Killzone, and Killzone doesn't bring in the Halo bacon.