I guess commitment is a vague word for some.
Maybe this is the reason why they just easily give up when they perceive some flaws or hardships in their present situation. They look for something much better when they fail to improve themselves to be better.

Then they begin to question your trust issue when many times you have given them chance to speak the truth.
How such a man values his ego and rather chooses to disrespect someone he thought is weaker than him.