Because the purpose of Murdoch`s BSkyB bid is essentially so that he can set up a UK version of America`s most popular news channel Fox News.
On Jerry Pournelle`s site, Neil Craig explains the business/political background
This is purely my opinion, but I believe the story, which has been quietly a well known secret for years with almost all papers, including the Guardian, which broke this, hacking at some time or another, is now such a major storm. The BBC`s virtual monopoly of British broadcasting is being threatened by Murdoch`s expansion of his control of Sky, the satellite broadcaster, so they are pushing this story hard.
Last night (Thurs) the BBC news was almost entirely devoted to the hacking story story; followed by Question Time where all the questions selected by the BBC except for 1 in the last 3 minutes were the same; followed by Andrew Neil on the same. 2 1/2 hours on this story and virtually none on the rest of the world`s news That would be justified if we were seeing a breaking news story like 9/11, but for nothing less.
Broadcasting in Britain is essentially a monopoly of the BBC and people they approve of. This monopoly is legally committed to "balance," but is in fact the propaganda arm of the British state (along with the Guardian, which survives on government advertising). Murdoch`s attempt to buy all of Sky would weaken that monopoly slightly.
I do not consider it a coincidence that this scandal, which journalists of all newspapers have been guilty of for years, has suddenly broken on Murdoch`s head alone."