So what is the reason? Often, I and a good few psychologists (I suspect) would say, is that often the person themselves cannot explain why, and resort to petty excuses that they 'think' are the reasons to allow them to continue. They shroud themselves in a shell of fabricated justification, not in a malicious manner, but simply because they're just as confused as to their feelings as anyone else, and find alternative explanations.
It's a shame really. No real good can come of such irrelevant conflict. It causes grief left, right and centre for the two parties involved and any others between and around them. Most importantly, perhaps, nothing is gained. No material or emotional satisfaction can be accrued in good conscience.
This is yet another reason tagged onto the long list of similar items explaining my long held neutrality obsession. It's the perfect standing, as far as I can see. If you don't stand against anyone, it often becomes infuriatingly hard for someone to stand against you, and you are free to amble peacefully through life.
I can only imagine what life would be like, if everyone tried their hardest to avoid conflict.