What causes Alpha decay?
The protons in a nucleus is held by strong force. Without strong force, the electrostatic repulsion between protons would not allow a nucleus to form.
The strong force is stronger than the electrostatic repulsion. That's why it can stop the protons from escaping.
However, the range of the strong force is short. This means that each proton can only feel the strong force of neighboring protons and neutrons. But, they can feel the repulsion from all the protons in the nucleus.
When the nucleus happens to get distorted in shape, the delicate balance between the strong force and the electrostatic force is upset. The electrostatic force dominates and some part of the nucleus gets to escape.