Have you ever been sitting around and thinking to yourself “I wonder why nothing but light can travel at the speed of light? What is so special about 300 million kilometers per hour?” I’m sure you do, if nothing else this has to be something that shoots through your head after the chipotle kicks in. That and perhaps what that bathroom graffiti is trying to say. “Larry Ez Hamo”, thanks I guess bathroom stall.
I look at the speed of light like you would look at the temperature in Kelvin. Kelvin has a lowest possible value, known as Absolute 0, this is the state where absolutely all movement has stopped. It is technically impossible because of the Heisenburg Uncertainty Principle (or that’s how I understand it) but it is there nonetheless. Basically the more motion in the particles the hotter something gets, the less motion the colder. But you can’t go into negative speeds (at least not in the most common understanding of speed) and because of this you have a minimum value of 0, no speed, frozen in space (and effectively frozen in time).
Now the speed anything can travel is relative to its mass, mass effectively creates an upper limit on how fast something can go. The reason that light travels at light speed is that it is effectively massless (I hear that light has infinite mass sometimes, but my understanding of it is that it lacks mass. So I’m going to stick with that and just caution you to read about these topics before taking my word as law).
Nothing travels faster than light because substances don’t have a negative mass. Again I’m sure there is an actual physics problem where negative masses are real, a real world version of irrational or non-real numbers thing. But for the sake of a basic discussion we will assume that mass is like temperature and it has a very real limit.
You can approach the state of 0 mass as much as you want without ever actually reaching that point. You could also likely reach 0 mass which would result in an incredible release of energy and probably suck (since you wouldn’t be turning back into an object with mass after). With that thought in mind you could very literally go out in a flash of glory.
This is why there is a light speed and this is why light travels at the same speed regardless of your point of observation. It is the maximum possible value because it has the minimum possible mass, any change would make it not massless and it would no longer be light.
So that would be my answer to the “Why”. As best as I can understand it this is why there is a light speed and why nothing else travels at this speed. Very same reason why nothing is colder than absolute 0.