Mathematics is inescapable. If you want to understand why the speed of light is constant, I don't know the answer to that, probably no one knows, or ever will.

I would say that the ‘acceleration’ of light is constant not the ‘speed’. In other words, when a photon is generated, it accelerates to the speed that the surrounding ‘continuum’ allows it to. The ‘continuum’ acts on photons like the air on a falling object. There is a constant ‘force’ that accelerates the ‘entity/photon’, depending on the density of the ‘continuum’ the speed of the ‘entity/photon’ is balanced by the ‘resistance’ of the ‘continuum’.

Anyway it’s a long story with lots of math and the explanation would become more confusing so I’ll stop for now.
On the other hand, if you can tell me how mass and space came into being, I will tell you why the ‘acceleration’ of light is constant.

Cheers