and apparently, it's getting stronger https://arxiv.org/abs/1811.02590
Any theory you come up with is better than Dark Energy being a thing. I have two:
If spacetime assigns gravity, then empty space doesn't have it ..so those regions would not have gravity wells. Empty space is like anti-gravity because it causes the spacetime fabric to be higher - which causes the gravity-wells/spacetime-clumps to coast/slide away from each other.
The edge of the universe is likely a sphere that keeps expanding like a balloon. I propose that gravity-wells of galaxies all move towards the edge of the sphere that they are closest to. This implies the sphere edge is something that pulls gravity wells towards it. It also says the sphere edge is likely the black hole we arrived in with enough gravitational force to pull galaxies towards it.
If we are not in a black hole, then the core of our universe has a density of spacetime that causes gravity-wells to slide towards the sphere edge.