Interestingly, Nicholas Watt at the Guardian tells us why. In an article about Lansley's possible future Watt says:
If Lansley leaves the cabinet he might be tempted to point out that he was keen to explain his reforms which were included in the Tory manifesto. He was, however, blocked by Andy Coulson who feared unsettling voters on the NHS ahead of the election.Coulson was a tabloid editor, he knew what the public wanted to hear, and he knew that Lansley talking in detail about his plans would be disastrous for the Tories' election plans. Considering that Cameron could not get a majority at the 2010 election, it is likely that talk of Lansley breaking up the NHS would have lost him seats. Ironically, it would have been the Lib Dems who would have gained, possibly giving them more seats than they have had for a century.
A lost opportunity for the Lib Dems.