French mine capacity preserved a compact sea-denial option

Why did France retain the ability of the Bretagne class to deploy 30 naval mines during refits?

The likely reason was that mines remained useful for denying an opponent access to constricted waters, especially in Far Eastern operations.

The suggested reason for retaining the 30-mine capacity is its usefulness for sea denial, especially in Far Eastern waters with limited room to manoeuvre. That explanation is offered as a likely motive for the French decision. Mines can prevent an opponent from using an area. They do not by themselves establish sea control, because the navy laying them also needs to be able to use the water.