They could be nice honeypot locations for the US to continuously monitor, to see who turns up with robotic submersibles. An early warning system for identifying actors with nuclear aspirations.
It's already enriched and comes with a working design.
For a non-nuclear nation, that would be all they'd need to become a nuclear nation.
Then blow it up in a test explosion to show the world, and then they could work slowly on making another bomb while bluffing that they have lots ready to go.
In fact, I wouldn't be surprised if someone hasn't already taken it, and left a dummy weapon in its place.
Sure, deep sea exploration by humans is hard... But using unmanned craft, they're mostly impervious to pressure.