Question

How did the four fundamental forces come to be?

Answer 1

They are the expression of our interpretation of currently observed physical phenomena.

Explanation:

The entire study of "physics" and much of "astronomy" are about trying to understand how the universe operates. When we reach the limits of our observational abilities or mathematical reasoning we call the starting points "fundamentals".

Our best observations to date are best modeled with the description of the "four fundamental forces". That may be it, or maybe we haven't really found the "fundamentals" yet.

At whatever level we are able to observe phenomena and conjecture interactions, we remain observers, not initiators. Thus, at best we could also only speculate on the "origins" - even assuming we had the right subjects.

The current speculation (and part of the search for the Grand Unification Theory) is that they are the "natural" outcome of the "Big Bang" initiation of the universe. Speculations about THAT event often cross over into religion rather than science.

Here's an example of one derivation:
https://archive.org/details/R.A.Zahedi1Forces.of.naturesLawsApr.2015