There's no good reason for it. Nothing breaks if you houserule it, but there isn't errata, either.
Basically, what happened is that it's a consequence of design by committee, which leads to inconsistencies like this. Whoever assigned Bone Lacing to be F figured that since it made your melee attacks do P damage, it should be forbidden, just like cyberspurs or whatever else. But Bone Density Augmentation and Cyberlimbs get you P-damage regular melee anyways, and it's not like actual melee weapons are all F.