Lance has been the most tested athlete in all of history for doping violations. In one year alone he received over 60, knock-knock-suprise (whether at home or in a hotel), random blood tests. He's never tested positive. The USADA has even admitted they don't have a positive drug test for him. The World Anti-Doping Agency and UCI, the two strongest international doping/cycling outfits have cleared Lance and actually forbid people from participating with the USADA's witch hunt... since they don't even have jurisdiction and the statue of limitations has expired. The Judge who tentatively allowed the USADA to have jurisdiction, even noted that the WADA and UCI have proper jurisdiction, but precariously gave it to the USADA as neither wanted to persecute Lance. Why would they, after twenty years, they've never found anything - and he was tested with everything they had relentlessly.
The USADA's only evidence against Lance is hearsay, hearsay from people they've admitted coerced into testifying by offering them immunity from their own doping convictions and of course people with huge vendetta's against Lance.
He simply doesn't stand to win anything by fighting the USADA. They technically don't even have authority to strip him of his Titles, that's another international body... although they can possibly coerce that group into it. They've been vocal from the start that they consider Lance already guilty, and that this is about proving their own legitimacy. Read some of their press releases, they're insanity. They're not going to hold a trial in front of an impartial jury, they're going to serve as judge/jury/executioner and have already stated he's guilty - without a single positive test result. If Lance goes through with challenging them he grants them legitimacy. Hell, the USADA's own statue of limitations has even expired and they're only grasping at the straw that they should be thrown out because Lance's is a liar, in their opinion, for stating he didn't dope. Even the judge called them out on that, but begrudgingly let them move forward.