There is actually simple explanation for both.

Submarine got lot of undeserved attention. In my country it is called "cucumber season", when basically non-event will get lot of coverage because lack of other events, usually during summer.

The migrant trawler has cynical, but simple explanation too. Refugee are coming to Europe since 2014. They are often behaving entitled towards Europeans, assaulting them, especially women and girls. Thus few of them drowning in the sea does not create any compassion in Europeans. It is ugly truth, but when my neighbor will be making my life living hell for years and then his house catches fire, I am not going to feel compassion either.