Why is the speed of light what it is and not something else?

Answer 1

Because it is. There's no fundamental reason that we're aware of why it should happen to have the precise value it does ... it just does.

One of the things physicists (especially cosmologists) have been interested in is figuring out if there's some underlying reason that certain physical constants have the values they do, or if they're more or less "random".

It turns out there IS a "reason" why some values are what they are, and that reason is "if they were very different, we wouldn't be here to ask the question." For example, if the color force were slightly stronger than it is, all the hydrogen in the early universe would have converted to helium ... and the universe would be full of helium and nothing else, making it impossible for us to exist.

This is called the "Strong Anthropic Principle", and it sounds a bit arrogant, but it's true: the universe is the way it is because it makes us possible. (The reason it's not really "arrogant" is that we're not necessarily saying that the universe had us in particular in mind when it was "deciding" what its physical constants should be ... just that the fact that we DO exist puts constraints on what the values could have been. Some cosmologists suggest that our universe is only one of many, and nearly all the others are dead, lifeless, boring places, because their physical constants are such that they preclude the development of life.)

Beyond the strong anthropic principle, there may well be fundamental reasons why the, say, fine structure constant is what it is (almost exactly, but not quite, 1/137). But we don't know what they are. Yet.

The speed of light is one of the factors in the fine structure constant, which is why it's particularly germane to your question. If the fine structure constant were different from what it is by more than about 3%, then stellar fusion could not produce carbon, and ... you guessed it ... we wouldn't be here to ask the question.