Why did France stop its uranium extraction activities?
It's cheaper to buy from a foreign site with a higher concentration of Uranium ore than mine it from an inferior mine in your own country.
Uranium ore is very common (40 times more common than silver and 500 times more common than gold) and can be found everywhere on the planet - even in the sea water. The concentration, however, makes some sites more economical than others.
For a price estimate, see e.g. List of countries by uranium reserves, which states:
As of 2015 646,900 tonnes of reserves are recoverable at US$40 per kilogram of uranium, while 7,641,600 tonnes of reserves are recoverable at $260 per kilogram.
France is listed as having zero tons of reserves at $260/kg, while they can buy it for much less.
The top three countries mining Uranium are Kazakhstan, Canada and Australia. This list includes several stable countries on which one can rely for a steady supply.
I bet France would restart it if they felt their supply was threatened.