He wants to. He wants to follow the success that the Wall Street Journal has had in getting subscribers to fork over money for the right to log onto the Journal's website. (And soon, to sign up for Journal micro-payments for web reading.) Murdoch wants to do that with his other news properties, but he won't be able to. Why not? Because most of other news outlets are junk.
I'll let Murdoch biographer Michael Wolff explain [emphasis added]:
[Journal editor Robert] Thomson is saying that it would be great if News Corp. could charge for its other websites like it's charging for the Journal. But it obviously can't because New Corp.'s other sites—the New York Post, Fox News, and at the Australian and British papers—are a joke. They're unmanned, unsupported, and, with technology that's often a decade old, they don't work. That is, except for the Journal, and, also, the Times of London, a site which Thomson ran before coming to the Journal and, not incidentally, got Murdoch to make a big investment in.