I've read much more than a simple Wikipedia article. And the only thing
I can come up with is that physicists can't explain the why either -
just that it's the way the math works out.
You just don't get it. A photon has no rest mass. It only has it's
engergy. If it had rest mass and had to be accelerated to the speed of
light not only could it not accelerate to c, it couldn't accelerate
instantaneously to *any* speed.
The only mass a photon has is that which is equivalent to its energy, E
= mc^2.