Why is the plasma state of matter essential for initiating nuclear fusion in stellar cores?

It allows nuclei close enough to overcome electromagnetic repulsion for the strong nuclear force.

Stars must exist as plasma because this state of matter, often called the fourth state, involves immense heat and pressure stripping electrons from atomic nuclei, resulting in a superheated, ionized soup of free electrons and charged nuclei. This ionized state is critical because the colossal internal pressure forces the atomic nuclei extremely close together. In normal conditions, nuclei possess a positive charge and naturally repel each other electromagnetically. However, the extreme proximity achieved within the plasma interior allows the powerful short-range strong nuclear force to overcome this electrical repulsion, enabling the nuclei to slam together and initiate the process of nuclear fusion.