It’s a result of compassion fatigue. When the first dead migrant children washed up on the Greek coast on people were appalled and transfixed. But the next month there were more dead bodies, and then more. Eventually people stop caring.
I’m old enough to remember “Live Aid”. When Bob Geldof got up on stage and said we were going to end world hunger people really believed it was possible. Since then there have been dozens more famines in Ethiopia, and the deaths run to the tens of millions. And now no-one mentions them.