Photons are carriers of vibrancy, or vibration, throughout our universe. The nature of a photon is rather curious. The more energy they contain, the smaller they are. This relates to their wavelike nature. Radio waves, for example, are comprised of photons which can be meters, or kilometers, long.
Microwaves are in the centimeter range.
Photons of light are tiny, by comparison, but X-Rays are smaller still. All of these manifestations move at the same speed, in a vacuum. The Earth's atmosphere allows some of the above to travel more quickly than others, but I don't think that this will lead us to the answer of our question. The reasons why light's speed is limited may not be found in our universe at all. In the world before our universe began, however, Science has asserted that light, as vibration or energy, would have very different properties.