Perhaps the main reason is that the particles that light consists of, photons, are massless. It's down to this that they have all these weird properties.
The fastest possible speed, according to the currently known laws of physics. Electromagnetic radiation exists in the form of waves or photons moving at the speed of light.
I must add: because we think its the fastest thing there is does not rule out something faster we just don't know of.....OR does the laws of physics not allow so??
The speed of light often (c) quoted at 300,000 km per second is only through a vacuum. Light passing through a diamond goes less than half as fast at 130,000 km per second. In fact the slowest recorded is through sodium at -272 degrees C at just over 60 km per hour. So it really depends!
Just as Einsteinian physics have supplanted Newtonian physics, we anticipate a day when our understanding may be expanded yet again to describe motion faster than the speed of light by an as yet un-discovered or un-reported set of physical laws.
There is no way to predict if it will happen in our lifetimes. I'm not betting on it.