Newtonian physics are a good approximation for big objects that move slowly
Like your mom
Why is it so hard for Kylo Ren to calculate a good approximation of where Luke Skywalker is?
Why doesn't Kylo Ren's lightsaber look like a normal lightsaber?
Because it's a First Order approximation.
They say physicists like to work with harmonic oscillation because it's the only problem they can solve.
That's not exactly true, but it is a good approximation.