Snuggling and launching drones from deep within enemy territory is a much more complicated op than a couple of dudes diving in the middle of nowhere.

Bringing that bridge down is also much harder than blowing up the pipeline, because the bridge is covered by a lot of defenses, and naval drones will always have limited payload (if they want to be fast enough to evade defenses). Dudes performing a dive in the middle of the sea far from the battlefield are much less vulnerable.