Why are newspaper headlines important?

To catch the eye and make some one want to read the entire story. The original intent was (and still is) to lure of a passer by at the news stand into buying the newspaper. This leads to some sensational headlines to what might be a mundane story.

This is still used in all forms of media. TV news has a "sting". "Two shot by suspected drug dealer, details at 11" is something one might hear on the TV between programs promoting the news. Headlines do the same thing.