Not specific to the proton, but "why are all particles of type X seemingly identical" is a question that physicists have asked. https://en.wikipedia.org/wiki/Id

Not specific to the proton, but "why are all particles of type X seemingly identical" is a question that physicists have asked. https://en.wikipedia.org/wiki/Identical_particles https://en.wikipedia.org/wiki/Identical_particles Sometimes with not-so-serious results: https://en.wikipedia.org/wiki/One-electron_universe https://en.wikipedia.org/wiki/One-electron_universe