Why does nuclear fusion only happen at extremely high temperatures?

To make fusion happen we need to bring the nuclei close enough for the short-range strong nuclear force to act. The nuclei are both positively charged so repel electrostatically. So we need very large thermal kinetic energies to do work against this repulsive force to bring the nuclei close enough to fuse.

Nuclear fusion is when two smaller nuclei join to make a larger nuclei. These nuclei are made of protons and neutrons. Since protons are positively charged (+) and neutrons have a neutral charge (0) the overall charge of the nuclei are positive. Because of this property when the two smaller nuclei attempt to join they repel one another, so then you would think how can fusion possibly occur ? well high temperatures allow this electrostatic repulsion to be overcome and allows the two smaller nuclei to fuse.