Doing all of that math and tracking them is a huge order. Outer Wilds famously simulates an entire solar system using Unity and they had an issue early in development where bugs would occur more frequently as the player visited the edge of the solar system due to floating point math getting wonky in the engine and the solar system's Sun being 0,0,0 coordinates. Their solution? Make the player coordinate 0,0,0 and everything else moves _around_ the player. That's right, in Outer Wilds, when you jump, the planet you're on is actually moving away from you. But they managed to use this method to simulate newtonian physics pretty well.

And even that solution is only temporary. Its possible to watch the simulation go on so long that planets begin to de-orbit the sun as the math simulation breaks down. For spoiler reasons players don't run into this issue, but it exists.

PS: If you haven't played Outer Wilds and you enjoy exploration/puzzle games go play it. Avoid spoilers if possible.