I think there's a couple of issues here.
First thing to say is that I'm so glad things are going so well for you, Jones. Sometimes an affair really does leave an improved relationship there in the long run and is a wake up call.
The first thing to say is that there are complicated reasons for Mumsnetters asking wronged spouses to doubt what they are being told or to consider leaving, and it not always about wanting them to 'LTB'. Strength is required for any course of action, frankly.
I think Jones story is brilliant and instructive. If you look at her thread, her husband behaved in exactly the way that a cheater should and does if they really really want to save their marriage.
Sometimes this doesn't happen and it makes it hard to know what to advise someone to do.
Sites like www.affairrecovery.com (which exclusively tries to help people STAY TOGETHER after an affair) cite that the most common regret of someone who has been cheated on when they look back is believing everything they were told initially and accepting immediately that they wanted it to work out. (This is by people who DID work it out, by the way, so it's not about regretting staying.) We have an honesty bias, particularly towards people we love, and a fear of change. When we want to hear something we try really hard to hear it.
However the truth is that most people who have affairs minimize the extend of what they did and how they felt about the other person (NOT ALL, MOST). This is to preserve the view of themselves but also not to hurt their spouse, who they may well love more. This CAN mean a very damaging months/years afterwards where the betrayed spouse discovers things that don't fit with the story they were told, or even when the cheater stays in touch with the lover, or carries on seeing them, because they feel such guilt about hurting them too. This makes it HARDER for a marriage to survive in the long-term than if the truth is forced out and insisted upon at the time, even when everything inside is telling you that they have chosen you and to brush it under the carpet. This is sometimes why posters question and push OPs to realize the extent of the infidelity acted against them, not to hurt them, but to make it possible for a marriage to survive and find a new honesty and intimacy, rather than continuing to hide behind deception.
As for the leaving part, well, that's the other major regret. Often those who've been wronged regret not forcing the cheater into a position where they really had to realize what they'd lost. And then the return back into the relationship is something the cheater has to 'fight for', and see objectively for what it is, not just an easy 'status quo'. It is likely, JOnes, that your husband knew you would leave if unsatisfied, that he respected and feared your reasonable response to his actions. Some partners quietly doubt their partners WOULD leave. And so they do not offer the apology and behavior that would allow the betrayed to recover. Because they don't need or want to. It's incredibly selfish but sometimes only their own loss is what motivates selfish people.
The betrayed spouse if often best served by realising that they ARE capable of being alone, that actually that would be okay, and so they, equally, made an active DECISION out of love and choice, to re-commit to the relationship, not one born of fear or ambivalence. Both the actions of questioning the truth of what you're being told, and imagining and experience life alone are ESSENTIAL for SOME people to actually re-commit to their marriage meaningfully. Rather than leave it.
I am not a LTBer at all. I want marriages to survive affairs if that's what both partners want. But I do encourage questioning and detached independence, because having been on both sides of an affair, they are the only things that worked for/on me, as the betrayed AND as the cheater.