Here's the thing that might make it easier to comprehend, from a much simpler perspective.
Scientists start out with a known fact. For example, things are pulled together with a force that is related to the distance between the objects. Also, electrical currents and objects with aligned metallic particles are "magnetic", and the resulting forces line up in a characteristic pattern.
They take these facts, and start dreaming up reasons WHY. They make theories.
The critical thing here is that while coming up with these theories, they must also have a way to TEST them. And that is why the wave theories are presented as how things like gravity work. They postulated that gravity forces act like waves, and then they came up with actual tests to see if during the test, the real world behaves the same as their theory predicts. Of the millions of theories people have come up with over many many centuries, the theories in the OP have "passed" the most tests. Some theories remain strange, yet they pass tests that support more than one theory. The best example is the wave/particle/uncertainty theories of light. You can measure the impacts of light photons on a surface, indicating that photons are particles. But if you shoot photos at 2 apertures, you get interference patterns on the other side indicating that those photons are acting like waves. Even more confusing, if you shoot a single photon at 2 apertures, you STILL get an interference pattern even though the photon could have only gone through one of the two apertures, indicating that at some level of physical size, the universe won't show it's hand regarding random events. This last one is part of the goofy world of quantum physics.
The point is that we STILL may not know exactly how that stuff works, and why. But we've come up with tests to see if our theories match what really happens. And when it comes to making practical applications out of theoretical physics, that's often good enough until the applications rely on exact theoretical perfection that the application doesn't work anymore, indicating that the original theory is either wrong or incomplete. At that point the theorists try to plug the holes in the theory or come up with a new one (as in Einstein explaining things that can't be explained with Newtonian physics, and Quantum theory explaining areas that can't be explained with anything that came before).
So don't get wrapped up in the conceptual details unless you actually work in those fields, because they are really just theories that have not yet been dis-proven by experiment. At some point, things like wave/particle duality of light and quantum effects will probably be integrated into a single theory. We're just not there yet.
