Temperature is a classical thermodynamics variable. Protons and neutrons belong to the quantum mechanical frame that became necessary to be studied when experiments showed disagreement with classical predictions . The photoelectric effect,black body radiation and the atomic spectra could not be explained or modeled with the classical mechanics and electromagnetic models existing at the time. Quantum mechanics was necessary in order to describe the experiments and has developed in the theory of the microcosm. Beginning with Schrodinger's equation and the Bohr model the theory has developed into the standard model of particle physics as the underlying quantum mechanical level of nature.
In the quantum mechanical level charge is carried by the charged elementary particles in the table and as they are point particles, cannot be split off from them, the value is fixed and any "motion" of charge has to follow the interactions of these elementary particles.
The simple answer to your question is: because the protons and neutrons are composite particles made up by quarks that carry the charge, which are bound together by the strong force, the proton and the neutron independently. A spill over of the strong force makes the strong nuclear force that keeps protons and neutrons in a nucleus. It takes the very high energies of the collider experiments to change a proton to a neutron. It can happen with the weak interactions depending on energy conservation, but the nucleus, because of the interaction, changes. See beta decay.
See this answer of mine for the complexity .