He'd already passed up two perfect opportunities to retire. The first, of course, was when he lost the Yellow Jersey because of getting busted for doping. There really was no coming back from that. But then you really can't blame a guy, no matter how disgraced, for holding out hope.
The second time was when he blew the lid off the whole pro racing game by coming clean - not about everything, I'm sure, but about enough. If there was any smidgen of hope for coming back after the bust, there wasn't one micron of possibility for getting a ride after this. Not unless Novitzsky & Co decided to sponsor a team - but then they'd never get an invite.
Pro cycling is what it is. Its more flagrant corrupt practices can be ameliorated, and they should be. (It would be great to see the UCI blasted into a million glittering fragments.) But it won't change fundamentally until its fundamental basis changes - from money, to sport. And that won't happen until society changes. And that's that.