Do people bully the weak to feel strong?

Yes. Most often the answer is a strong yes.

People bully when they are feeling less than or inferior or have confidence issues, life issues, etc. to build themselves up and make themselves more prominent and have a purpose, meaning and value. It makes them seem like they have power, control and purpose but it just shows weakness in the long run.

Reference: https://www.quora.com/Do-people-bully-the-weak-to-feel-strong