I don’t know if he genuinely didn’t understand or if he was too embarrassed to admit to a mistake
Worse, he actively lied. In his edited video about the petition he actively misrepresents the initiative, then goes on to edit out the the part of Ross' video that would have contradicted his misrepresentation.
This is not an innocent or negligent mistake on Thor's part, it's an active attempt at burial.
See here's the thing: a person who is able to rationalise something morally unjustifiable once, will be able to do it again.
By cheating you showed everyone you have no real spine to speak of, you can rationalise it all you like (that's part of the problem) but the reality is that when you had the choice to break up and pursue the other person or not and cheat, you managed to talk yourself into accepting betraying the supposedly most important person in your life.
Moreover, there is absolutely no way for you to ever prove you won't do it again until you die, and even then some people will still be skeptical even if you never do it again, and they'd be correct to be.
You may have grown a sense of respect for other people's trusts, or you may have gotten better at cheating, or your boyfriend may have settled for a serial cheater and decided to turn the other way.
Either way they are trying to spare him from this AND to prevent society at large from accepting cheaters back into relationships because nobody, not even cheaters like you, wants cheating to be done to them, and making it something you can come back from makes it more likely.
ETA: given your post history, this one especially, you probably are getting shat on simply because you, specifically, deserve it, not because people hate cheaters in general (though we do).
Your first post on this topic is literally a thinly veiled "Why would my mid-ass boyfriend not take me back? He's mid and I am letting him fuck me, why would he think he deserves better?"
The answer was in the post history all along: people are telling him to drop you because you are lower than pond scum and they see through you. I pity him for being indeed mid and spineless enough to have accepted you back.