"Couldn't there exist different laws of gravity for big things like planets and small things like rocks, which explains why I've never seen rocks attracted to each other?"
Yes, there could in some alternative universe, but not in this one that we know of, and it's not necessary to explain why you don't notice rocks being attracted to each other.
There could exist some difference between "microevolution" and "macroevolution," but not in this universe that we know of, and it's not necessary to explain species.
The entire concept was made up by creationists to try to add a patina of science to their deeply-unscientific beliefs. And the problem with an unscientific world view is that science will never change your mind about things, you'll just decide what science to accept and which to not accept.
Something very related is a topic that is seriously discussed among physicists:
> https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
The problem with the existing theories of gravitation which seem to work quite well on the scale of solar systems is that there does seem to exist evidence that some observed data on the scale of galaxies might not be well-explainable by these theories. See
> https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Ob...
Very recently new evidence for MOND came up:
> https://phys.org/news/2023-08-smoking-gun-evidence-gravity-g...
> https://news.ycombinator.com/item?id=37051241
See also:
> https://tritonstation.com/2023/08/02/is-ngc-1277-a-problem-f...
Even from a biological perspective this distinction is not nonsense: couldn't there exist an additional mechanism that is not arbitrary mutation and survival/selection of the fittest, which could be an additionally important for the formation of species and macroevolution?
Candidates for such possible additional mechanisms have been proposed from biologists, such as Lamarckism or epigenetics (though the mainstream view in biology is these either could not be observed (Lamarckism) or are not considered to be important for macroevolution (epigenetics)).