Of course we need journalists, but it's just as good that we have some independent fact checkers that also have a platform to stand on.
And it's not like the network journalists have done anything to earn our trust recently.
And one answer to your second question could be: money. Professionals need to generate (exactly) 60 minutes of news every night (minus time for commercials), and have it be entertaining enough to get people to watch (so they can sell more commercials). Amateurs providing random facts on the internet are not dependent on other corporations to generate income, or daily TV/newspaper deadlines.
Thought experiment: if we didn't have a profession called "journalism" today, and free worldwide publishing already existed (i.e., the internet), would we wish that they existed? Would people be saying "For the sake of our democracy, we need to pay these random Reddit fact checkers a good salary"?