Couldn’t it be a byproduct of frame dragging? Any massive object that spins is pulling stuff into it by forcing things to rotate in some kind of space time whirlpool?
This means if something massive doesn’t spin, it would have no gravity, but isn’t everything large enough to have gravity in space pretty much spinning?
No, many asteroids have detectable, "functional" (e.g. they pull dust towards them) gravitational fields, but are not spinning like planets.
Given that we can experimentally observe the gravitational attraction between two non-spinning objects in a lab, I don't think that's the answer.
Descartes had a similar idea, but as far as I remember, it requires ether.