Okay, I’ll do it “Aren’t submarines supposed to sink?”
Nope
Don’t know if this one is of the same design.
I’ve been on similar tourist subs in several different countries.
In their normal configuration, they are slightly buoyant. They need to use thrusters continuously to stay submerged. In the event of power failure, it automatically returns to the surface.
They also have a substantial jettisonable ballast as well in the event of flooding.
I’ve seen two articles on this accident from separate sources. Still not clear what actually happened.