The Saphir and Perle are attack submarines - they aren't France's nuclear missile subs (that's the Triomphant class, and they have 4 of them for exactly the rea

The Saphir and Perle are attack submarines - they aren't France's nuclear missile subs (that's the Triomphant class, and they have 4 of them for exactly the reason you described). France "needs" all this equipment because France (or least enough of its governments) have decided that it's important for France to have an independent capability to influence the world beyond "soft power". It's easy to understand why they might want an independent SLBM force. And if you're going to be building nuclear submarines, may as well make nuclear attack subs so you can try to keep the knowledge and industry base more continuously active.