Sharing opportunities is a choice, and while some choose not to, others want those around them to benefit from the opportunities they themselves have gained. The biggest factor determining these behaviors is again the behavior of their environment.
It's a fact that the environment greatly influences people. It's not the same to surround yourself with criminals as it is to surround yourself with entrepreneurs who own businesses, look for new ways to make money, and obviously have neither the intention nor the time to wish ill on others.
One thing that has a huge influence is envy towards others. Those who take advantage of opportunities that others missed and refuse to share them are not only selfish, but also envious. Those who share opportunities for improvement with others demonstrate not only that they are good people, but also that they truly want others to succeed.
Only by reducing the likelihood of failure in people does ill intention in human beings decrease, but how do we get there? It's difficult; humanity still has many shortcomings when it comes to social progress. It's a cultural problem; that's where it all stems from, because opportunities are often concentrated only within specific groups.