Society has progressed way faster than our biology
Limiting beliefs, and perhaps all beliefs, are a perfect example of this. Limiting beliefs were helpful when we had to quickly learn not to mess with wild beasts and not to eat certain plants. 'Sabretooth tiger = possible death' is a useful limiting belief. That belief would actually keep a human safe. Limiting beliefs were also useful in tribal relations. They served as a way to reinforce tribal norms and group cohesion. But that is not the world we live in anymore.
In Today's World,
limiting beliefs only hold us back from being happy and successful. They cause us to reduce the options we have in life. If someone believes 'they always fail,' they probably will not pursue a genius business idea. My fear of abandonment led me to end relationships because I was afraid they would abandon me. Crazy, right? Limiting beliefs convince you to do crazy things in order to prevent possible suffering. Limiting beliefs have a way of making exactly what you are afraid of, happen.