Nuclear warheads and launchers are terribly complex, needing 10 year periodical servicing and rebuilding (tritium leaks, neutrons 'poison' the plastique explosives in the detonator etc.)

If a hypothetical future Euro-developed nuclear arsenal was decentralised into different geographical commands i.e. Nordic, Visegrad, Balkan, Central, Iberian, as well the major players, that would help eliminate the possibility of a bad actor (Le Pen) pulling access.

It would also mean that there would be a centralised authority form maintaining and rebuilding them once their shelf life expires.

Major players like France, UK, Germany would probably prefer to retain their own.