Yeah, I know about light being slowed down through various media and all that. My question is WHY gravity takes any time to operate. And just saying lightspeed is "the limit" doesn't work. Until we know how gravity really works, we can't tell the speed.

That is explained in quantum relativity. Entanglement in quantum theory. You can get instantaneous change (a paired photon, has indeterminate status, until the other member of the pair is measured ... before that they are both indeterminate). The classical view of omniscient objectivity is the sound of one Schroedinger Cat dying. However, you can't use entanglement to communicate (unfortunately).

Everything else, change moves at "c" or less (see relativity theory). It gets deep. Feynman said, anyone who claims to understand quantum theory (he meant the relativity kind) doesn't know. The simplest level is the Dirac Equation, and I posted on that. Crickets of course. Velocity isn't ... velocity. There is phase velocity and group velocity, even without the relativity complication.

Yes, that is the problem with explanation. Gravity explains falling apples, but what explains gravity? Well we had Newton's explanation (but he admitted it wasn't an ultimate explanation). And we have Einstein's explanation (he tried to find an ultimate explanation and failed). With epistemology, if not the world, it is professors (not turtles) all the way down.