I think the key word is capability. Everyone who is capable of being deployed receives X Factor, even if they might be screened or otherwise in the wrong place. Those who are incapable, who benefit from being able to live a relatively normal life where they can make plans in excess of 6 months, do not receive the X Factor while they remain undeployable because it is compensation for maintaining readiness.
The underlying point is X Factor could be used as a direct incentive for people to fulfil the military role that they signed-up for, where there is currently no incentive, and in actual fact many disincentives.
I think we all know people who can't deploy anywhere because they're medically downgraded, who can seemingly manage physical activity on their own terms - and often stuff more demanding than anything they would encounter at our less dangerous deployment locations (Qatar, FI etc). It's time to counter human nature with human nature - playing the game = extra cash; not doing so = out of pocket.