Probably 1.0-issues, retainers, squadrons... all of those being some hinderance to this change that seems just completly pointless to me. Why does it matter if a lancer can equip the Shinryu EX weapon just as much as a Dragoon can? If its more effort for them to remove those options than it is to keep them there, why remove them?
I just dont see a good reason to bother with this in the first place - other than maybe to force people to get and use their jobcrystal, but even that argument seems like uneeded handholding and babysitting.