They accept the sometimes unpleasant task of being the bearer of bad news. Reporting presents the opportunity to test assumptions, reveal previously unseen connections, and create knowledge. It takes viewers, listeners, and readers where they won't or can't go on their own. It holds the powerful accountable. It gives voice to the voiceless.
Journalists do what no other professionals do in a free society.
Know where to go to collect relevant documentation. Organize, sort, and analyze lots of sometimes conflicting evidence. Find, develop, and maintain sources. Recognize a lead and know how to follow it. Enable reluctant sources to talk.