But I am seriously thinking hard on the "land of limbo" dwellers, why they suffer in silence and why they stay there?
Is it self esteem? Self confidence? Emotional immaturity? Or are there other aspects that I just don't get?
Sorry but feel I want and need to analyze this a bit further as it could reveal more about how and why cheaters become cheaters.
It mostly reveals things about cheaters as it relates to their interactions within the marriage. Many cheater traits are internal and don't reflect on the spouse, though cheaters will exploit weakness. Every person is different, every relationship has two people, and every infidelity story involves even more people. Then you have the family background, upbringing, character, etc... it's very complicated. You could drive yourself mad trying to figure out what caused one person to cheat, let alone trying to explain the entire phenomenon.
With regards to limbo, I think all of those things you mentioned can be a factor. At a certain point the person you're with becomes all you know, and the devil you know is better than the devil you don't know. Uncertainty and fear lead to complacency, time goes by, nothing changes, they both care and do less for each other. It's a necrotic situation to be sure.
People should not accept that kind of situation, and maybe they don't at first, but the talks and fights that seem to bring resolution only last long enough to bring false hope and keep the relationship on life support. Whether they're scared of losing their partner or scared of being alone/finding someone new, these people should really be scared of wasting away their life away in an unhappy existence.
In reality, standing up for yourself and your relationship standards does one of two things: It scares your partner into making real and necessary changes out of fear of losing you, or it allows you to move on without that person (who turned out not to be your "partner" after all).