OP is aware that it does exist. In quantum physics, a lot of the questions of "why does it exist" are difficult to overcome. The answer simply is "it just does."

We can prove the math, we see the experimental evidence. The math comes long before the experiments. The problem is that "why" doesn't work at this scale.

For a frictionless spherical cow in a vacuum, if you apply a force vector to it, it will accelerate in that direction, until you stop applying the force; at which point it will continue on that vector at the last velocity it reached. "Why" this occurs is do to energy, and energy conservation.

"Why do massless fermions spontaneously break chiral symmetry?" We can prove it through the math, we can experimentally observe it. But "why" doesn't have a real answer. The answer is "it just does."