We now live in an age of 24-hour reporting of news and are being bombarded with innumerable bits of information and soundbites that need processing. IMO Twitter is by far the most onerous of these soundbite machines. This is a time of information saturation. Yesterday's news is being rapidly discarded in pursuit of the next new thing.
Wikipedia's entry offers a critical assessment of the phenomenon:
According to former journalists Bill Kovach and Tom Rosenstiel, 24 hour news creates ferocious competition among media organizations for audience share. This, coupled with the profit demand of their corporate ownership, has led to a decline in journalistic standards.
With little time to react, there is little time for research, and the perpetual risk that somebody beats them to the story. So they run a story, even with incomplete information, which makes the news vulnerable to disinformation and propaganda. The result is a poor quality of reporting even without companies enforcing policy as US networks did by removing troublesome journalists for the crime of not sticking to network narrative.
With all that information around - a fact lost on many a twitterer - journalists need to have an a attention span beyond a 24-hour news cycle. It is hardly an impossible task: The internet makes yesterday's news available through tools like Google.