He isn't wanting to go back to road racing - all that is finished. He wants to compete in triathlons and marathons, and organisers who have signed up to the USADA/WADA code of conduct won't let him while the lifetime ban from any competition lasts. While he denied that he doped during his comeback, there are dodgy blood values and USADA reckons that the chances that he didn't are one in a million.
A condition for shortening the ban is that he tells ALL the truth, which he doesn't want to do, because he could lay himself open to prosecution for fraud, and because he will look even worse that he does now having supposedly confessed all. USADA has given him until 6th February to respond to the offer to reconsider the lifetime ban in exchange for the truth, the whole truth, and nothing but the truth. The offer is only to reconsider, not lift the ban altogether, so whatever he does he's going to be out for at least another two years and probably longer.
Other competitors would be put in an impossible position. They might not want to race against him but if he is allowed to compete the only thing they could do is not compete themselves, which is not fair on them.
If he was allowed to compete and no one else competed - then it would surely be a hollow victory.
It wouldn't be fair for the other competitors but if they all didn't compete then maybe it would be a clear message that there is no point in racing against a cheat, it isn't impossible to call effectively a strike
He competed in huge marathons (New York, Boston) thousands of people take part in. Many of them would be running for charity as they do in the London marathon. For elite athletes their times are important for things like Olympic qualification. Why should they have to give all that up for the sake of making a point about Armstrong? Who is the one in the wrong here?