I think the answer is the same one for nearly every why are aeroplane systems still stuck in 1970.
Certification costs.
Then you can add extra weight and the fact that nearly all power plants are american and they are probably using refrigerants that are banned in the EU.
Finally I would not want to be sat behind a hydrocarbon filled a/c system even if it was retarded so it didnot explode but just burnt well instead.