Because some of them are, and should be, blatantly overpowered. I thought there should be a reason why the fighters tend to engage in fist fights some of the time, rather than blasting away at all times - because they can run out of power points.
I don't think I included the ability to augment some of the maneuvers with higher PP costs in the standard rule (will later; some of them already have 'super augmentation', like spirit bomb and amplify, which corresponds to the show), as is the case with powers - obviously these maneuvers are special since they work like both powers and maneuvers.
If you want to work with the fluff, you could call them 'ki/chi points' instead, although the ninja comparatively depends on very few ki points.