I think it's that we already know the outcome of the migrant boat sinking. The only thing to cover is the circumstances that led to them being on the boat and how to fix that which is politics and most people don't find that appealing.
Like you said the sub thing doesn't happen every day it's intriguing and edge of your seat cliff hanger ever hour that gets people's attention. It's man fighting against nature to try and save one of their own. It's like baby Jessica trapped in the well, miners stuck in a collapsed mine or those soccer kids stuck in a cave. People are paying attention because they want to know the ending.
It's kinda of like wondering why a marvel popcorn movie is doing better box office than dramas.