Sir Dave's "winning clean" mantra was bs from day 1, and anyone with knowledge of pro-cycling knew it. The Lance Scandal made it clear to everyone outside of cycling that to win, you have to dope. This put Sir Dave in a tricky position as reputation and public appearance is everything in his position so after chatting with his buddy, Tony Blair's spin doctor Alistair Campbell, he doubled down basically.
The interviews were as much public PR as investigative. Sir Dave kept his job, the public apperance was reinforced and Sky was distanced from "toxic Lance".
Edit - forgot to add, of course this was done with no pressure what so ever from the Murdochs at Sky.