The second hand 127/54 Oto Melara were cheaper
They were for sure refurnished before mounting them on the De Zeven Provinciën class. See e.g. The Naval Institute Guide to Combat Fleets of the World. It is also mentioned in the Dutch Wikipedia article:
Quote:
Nadat men besloot niet twee, maar vier schepen te bouwen koos men voor een Otobreda kanon van 127 mm. Vier daarvan waren overbodig geworden bij de Canadese marine na de verbouwing van de fregatten van de Iroquois klasse.
https://nl.wikipedia.org/wiki/De_Zeven_Provinci%C3%ABnklasse_(fregat)The last sentence means that the guns became available because of the rebuilt of the Iroquois class. The English Wikipedia article is not very detailed.
If you consider something like that unlikely: also the earlier Tromp class air defence frigates had old 120 mm guns from the destroyer
Gelderland. The re-usage of guns is a common praxis for many navies. Does not have e.g. the Canadian Navy still has some 40 mm Bofors from World War Two still in service? For sure on new mountings?