Some people haven't. Some people don't live in London but have relatives and friends who do, who they may be intensely worried about.
Some people don't have the opportunity to sit and watch the news bulletins all day and if they were to turn on the television or radio and the news wasn't there to give them information about the location of the explosions, the numbers of dead and injured and emergency numbers to call, the media would not be doing their job.
This may be a man-made atrocity rather than a natural disaster but there is no reason to give it less coverage than an earthquake or a tidal wave might receive.
And I might add that the terrorist's aim is a climate of fear which empowers him to achieve his political goals.
Distribution of accurate information does more to encourage informed discussion and dispel any climate of fear than attempts to muzzle the press - which will only lead to the spread of rumours, half-truths and paranoia.