I think the issue is the resources dedicated to each disaster. I don’t know if all the immigrants died though, so there may not have been a point in rescuing them at all.
There have been plenty of resources dedicated to rescuing the migrants. Over 100 have been rescued.
A big issue in the news coverage is that the migrant boat sank in the Ionian Sea in the Mediterranean. The Titan submersible was off the coast of Canada. So the news coverage in America largely focused on the thing happening near America. Same with the search and rescue. The US and Canadian coast guards were deployed for the search.
The Greek coast guard ran the search and rescue for the migrant boat since it happened off the coast of Greece.